The Cytoscape User Manual copyright is owned by The Cytoscape Consortium, and is made available under the same GPL license as Cytoscape itself: LGPL 2.1, the GNU Lesser General Public License, version 2.1, February 1999 available in text at http://www.gnu.org/licenses/lgpl-2.1.html.

Copyright (c) 2001-2015 The Cytoscape Consortium

Cytoscape @version@ is the latest version of Cytoscape, building upon the new architecture, developer API and set of user controls established in the 3.x series. If you're familiar with former versions of Cytoscape, this version will feel completely familiar and you'll be all set to go. In future releases, we will continue to tweak and improve both the software and the documentation. This manual will be updated to reflect all the latest changes.

This manual describes the installation and use of Cytoscape. For a more thorough understanding of Cytoscape and its ecosystem, we highly recommend reading the Welcome Letter accessible on the http://cytoscape.org website.

Cytoscape is a Java application verified to run on the Linux, Windows, and Mac OS X platforms. Although not officially supported, other UNIX platforms such as Solaris or FreeBSD may run Cytoscape if Java version 8 or later is available for the platform.

System requirements

The system requirements for Cytoscape depend on the size of the networks you want to load, view and manipulate.

Note that as of Cytoscape v3.2, networks are loaded faster and in less memory than with previous versions. While this is good news, networks created on v3.2 on a given memory configuration (e.g., 1GB) may not be loadable by prior Cytoscape versions on the same memory configuration.

Specific system requirements, limitations, and configuration options apply to each platform, as described in the Release Notes available on the http://cytoscape.org website.

Getting Started

Install Java

Cytoscape requires Java 8 or later.

• While Cytoscape versions prior to v3.2 run on Java 6, Oracle and other JVM suppliers have dropped Java 6 support. Consequently, Cytoscape v3.2 and later don't support Java 6 either. With v3.3, we have also dropped support for Java 7 for the same reason.
• We recommend a 64 bit Java Runtime Environment (JRE). While Cytoscape runs with 32 bit Java versions, using a 64 bit Java allows the largest networks to be loaded and enables the fastest network processing. For Windows, the default JRE download provided at java.com is 32 bits regardless of the Windows version. While Cytoscape will run with a 32 bit JRE, it will be limited to loading only small networks. We recommend downloading and installing a 64 bit JRE.
• We currently recommend only Java 8.

For additional information, select the Release Notes button on the Cytoscape web site (http://cytoscape.org).

Install Cytoscape

Downloading and installing

There are a number of options for downloading and installing Cytoscape. See the download page at the http://cytoscape.org website for all options.

• Automatic installation packages exist for Windows, Mac OS X, and Linux platforms -- best for most users.
• You can install Cytoscape from a compressed archive distribution.
• You can build Cytoscape from the source code.

• You can check out the latest and greatest software from our Git repository.

Cytoscape installations (regardless of platform) containing the following files and directories:

The p/ directory signifies the program directory, which varies from platform to platform. For Cytoscape to work properly, all files should be left in the directory in which they were unpacked. The core Cytoscape application assumes this directory structure when looking for the various libraries needed to run the application.

The u/ directory signifies the user's home directory, which varies from user to user and from platform to platform. To change the user home directory from the default, one can set the Java environment variable user.home to the desired directory -- this is useful when Cytoscape is installed on a workstation, but the home directory is stored on a central file server. user.home can be set by adding the following option to the Cytoscape.vmoptions file or the _JAVA_OPTIONS environment variable, substituting the desired path as appropriate:

• -Duser.home=/path/to/desired/home

Your operating system may have other mechanisms for setting environment variables -- see your operating system documentation for further details.

A quick note on upgrading your Cytoscape installation

If you have a previous Cytoscape installation you have two options:

1. Starting with a clean slate. For this you should delete your previous installation directory and the CytoscapeConfiguration directory (see below for the location of this directory).

2. Just keep what you have and simply pick a distinct, new directory for installation. In the unlikely event that you should encounter any problem, delete the .props files in your CytoscapeConfiguration directory. If that doesn't help try deleting the CytoscapeConfiguration directory. This latter step will cause you to lose all of the apps that you have installed via the App Store, so only do that if you are having problems or if you don't mind reinstalling your apps. The core apps will not be affected by this step.

Launch the application

As with any application, launch Cytoscape by double-clicking on the icon created by the installer, by running cytoscape.sh from the command line (Linux or Mac OS X) or by double-clickinging cytoscape.bat or the Program Launch icon (Windows).

After launching Cytoscape a window will appear that looks like this:

If your Cytoscape window does not resemble this, further configuration may be required. Consult the Release Notes available on the http://cytoscape.org website.

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Note on Memory Consumption

For most regular users, Cytoscape will estimate and reserve the proper amount of memory. An incorrect estimate may result in Cytoscape hanging at startup or Cytoscape unable to load your network. Unless Cytoscape fails to start or open your network, it has likely estimated the available memory correctly, and you can continue to the Quick Tour. If Cytoscape misjudges the memory size or can't allocate enough memory, it could be that you're running with a 32 bit JRE and could get better results by installing a 64 bit JRE -- see the Install Java section above.

When Cytoscape starts, it displays the current memory usage in the lower right corner of the main interface. You can click on the Memory button at any time to access an option to Free Unused Memory. While most users won't need to use this option, it can be useful for users who have multiple large networks loaded.

Overall Memory Size for Cytoscape

By default, Cytoscape uses an estimate for initial and maximum memory allocation based on your operating system, system architecture (32 or 64 bit), and installed memory. You can change Cytoscape's initial and/or maximum memory size by editing the Cytoscape.vmoptions file, which resides in the same directory as the Cytoscape executable. The file contains one option per line, with each line terminated by a linefeed, and an extra linefeed at the end of the file. Note that for the MacOS platform, the situation is slightly different -- if you are launching Cytoscape by clicking on the Cytoscape icon, you must edit the .../Cytoscape.app/Contents/vmoptions.txt file instead. To access this in Finder, you will need to right-click the Cytoscape app icon and select "Show Package Contents", which will display the Contents subdirectory that contains vmoptions.txt.

For example, if you want Cytoscape to initially allocate 2GB of memory and use up to a maximum of 4GB, edit the Cytoscape.vmoptions file to contain the following lines (... do not forget the linefeed at the end of each line, and an extra linefeed at the end of the file!):

• -Xms2GB

  -Xmx4GB

Stack Size

There is one more option related to memory allocation. Some of the functions in Cytoscape use larger stack space (a temporary memory for some operations, such as layout). Since this value is set independently from the values above, sometimes layout algorithms fail due to an out of memory error. To avoid this, you can set a larger heap size for Cytoscape tasks by using the taskStackSize option in the cytoscape3.props file (located in the CytoscapeConfiguration directory). This can be edited within Cytoscape using the Preferences Editor (Edit-Preferences-Properties...) - look for taskStackSize. The value should be specified in bytes.

Cytoscape recognizes a number of optional command line arguments, including run-time specification of network files, node and edge data files, and session files. This is the output generated when Cytoscape is executed with the "-h" or "--help" flag:

usage: cytoscape.{sh|bat} [OPTIONS]
 -h,--help             Print this message.
 -v,--version          Print the version number.
 -s,--session <file>   Load a cytoscape session (.cys) file.
 -N,--network <file>   Load a network file (any format).
 -P,--props <file>     Load cytoscape properties file (Java properties
                       format) or individual property: -P name=value.
 -V,--vizmap <file>    Load vizmap properties file (Cytoscape VizMap
                       format).
 -S,--script <file>    Execute commands from script file.
 -R,--rest <port>      Start a rest service.

Any file specified for an option may be specified as either a path or as a URL. For example you can specify a network as a file (assuming that myNet.sif exists in the current working directory): cytoscape.sh -N myNet.sif.

Note: if there are spaces in the file path, be sure to put quotes around it: cytoscape.bat -N "C:\Program Files\Cytoscape\sampleData\galFiltered.sif".

Or you can specify a network as a URL: cytoscape.sh -N http://example.com/myNet.sif.

All options described above (except for starting a REST service) can be accessed from the menu once Cytoscape is running.

Welcome Screen

When you start Cytoscape, you can access basic functions from the Welcome Screen:

The Welcome Screen is designed to access commonly used features of Cytoscape including:

• Create new network
• Import network
  • From file
  • From public database
• Import interactome for model organisms
• Open recently used session file

Also, a news panel always display latest information for users. For information on user privacy, see the Cytoscape Privacy Policy.

Basic Features

When a network is loaded, Cytoscape will look similar to the image below:

Most functionalities are self-explanatory, but we'll go through a concise explanation for clarity. The main window here has several components:

• The Menu Bar at the top (see below for more information about each menu).
• The Tool Bar, which contains icons for commonly used functions. These functions are also available via the menus. Hover the mouse pointer over an icon and wait momentarily for a description to appear as a tooltip.
• The Network Panel (Network tab of the Control Panel, top left). This contains an optional network overview pane (shown at the bottom left).
• The main Network View Window, which displays the network.
• The Table Panel (bottom right panel), which displays columns of selected nodes and edges and enables you to modify the values of column data.

The Network Panel and Table Panel are dockable tabbed Panels. You can undock any of these panels by clicking on the Float Window control in the upper-right corner of the CytoPanel. This is useful when you want assign the network panel as much screen space as possible. To dock the window again, click the Dock Window icon . Clicking the Hide Panel icon will hide the panel; this can be shown again by choosing View → Show and selecting the relevant panel.

If you click this control, for example on the Table Panel, you will now have two Cytoscape windows, the main window, and a new window labeled Table Panel, similar to the one shown below. A popup will be displayed when you put the mouse pointer on a cell.

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Note that Table Panel now has a Dock Window control. If you click this control, the window will dock onto the main window. For more information on the panels in Cytoscape, see the Panels section.

Network Editing

Cytoscape also has an edit functionality that enables you to build and modify networks interactively within the network canvas. To edit a network, just right-click on the open space of network window, select the menu item Add → Node, a new node will be added to the canvas. To add an edge, right click on a node, choose the menu item Edit → Add Edge. Then select the target node, a new edge will be added between the two nodes. In a similar way annotation objects can be added; pictures, shapes or textboxes; much like in MS PowerPoint or similar software. Detailed information on network editing can be found in the Editing Networks section.

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The Menus

File

The File menu contains most basic file functionality: File → Open for opening a Cytoscape session file; File → New for creating a new network, either blank for editing, or from an existing network; File → Save for saving a session file; File → Import for importing data such as networks and data; and File → Export for exporting data and images. File → Export → Network View as Graphics lets you export the network in either JPEG, PDF, PNG, Post Script or SVG format.

File → Recent Session will list recently opened session files for quick access. File → Run allows you to specify a Cytoscape script file to run, and File → Print Current Network... allows printing.

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Edit

The Edit menu contains Cut, Copy and Paste functions, as well as Undo and Redo functions which undo and redo edits made in the Table Panel, the Network Editor and to layout.

There are also options for creating and destroying views (graphical representations of a network) and networks (the raw network data – not yet visualized), as well as an option for deleting selected nodes and edges from the current network. All deleted nodes and edges can be restored to the network via Edit → Undo.

There are also other editing options; Remove Duplicated Edges will delete edges that are complete duplicates, keeping one edge, Remove Self-Loops removes edges that have the same source and target node, and Delete Selected Nodes and Edges... deletes a selected subset of the network. Rename Network... allows you to rename the currently selected network.

Editing preferences for properties and apps is found under Edit → Preferences → Properties.... More details on how to edit preferences can be found here.

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View

The View menu allows you to display or hide the Control Panel, Table Panel, Tool Panel and the Result Panel. It also provides the control of other view-related functionality.

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Select

The Select menu contains different options for selecting nodes and edges.

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Layout

The Layout menu has an array of features for visually organizing the network. The features in the top portion of the network (Bundle Edges, Clear Edge Bends, Rotate, Scale, Align and Distribute) are tools for manipulating the network visualization. The bottom section of the menu lists a variety of layout algorithms which automatically lay a network out.

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Apps

The Apps menu gives you access to the App Manager (Apps → App Manager) for managing (install/update/delete) your apps and may have options added by apps that have been installed. Depending on which apps are loaded, the apps that you see may be different than what appear here. The below picture shows a Cytoscape installation without installed apps.

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In previous versions of Cytoscape, apps were called plugins and served a similar function.

Tools

The Tools menu contains advanced features like the Command Line Dialog, Network Analyzer, Network Merge and Workflow.

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Help

The Help menu allows you to launch the online help viewer and browse the table of contents for this manual (Contents).

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The Citations option displays the main literature citation for Cytoscape, as well as a list of literature citations for installed apps. The list will be different depending on the set of apps you have installed.

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The Help menu also allows you to connect directly to Cytoscape Help Desk and the Bug Report interface.

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Network Management

Cytoscape allows multiple networks to be loaded at a time, either with or without a view. A network stores all the nodes and edges that are loaded by the user and a view displays them.

An example where a number of networks have been loaded is shown below:

The network manager (in Control Panel) shows the networks that are loaded. Clicking on a network here will make that view active in the main window, if the view exists. Each network has a name and size (number of nodes and edges), which are shown in the network manager. If a network is loaded from a file, the network name is the name of the file.

Some networks are very large (thousands of nodes and edges) and can take a long time to display. For this reason, a network in Cytoscape may not contain a "view". Networks that have a view are in normal black font and networks that don’t have a view are highlighted in red. You can create or destroy a view for a network by right-clicking the network name in the network manager or by choosing the appropriate option in the Edit menu. You can also destroy previously loaded networks this way.

Certain operations in Cytoscape will create new networks. If a new network is created from an old network, for example by selecting a set of nodes in one network and copying these nodes to a new network (via the File → New → Network option), it will be shown immediately follows the network that it was derived from.

The available network views are also arranged as multiple overlapping windows in the network view window. You can maximize, minimize, and destroy network views by using the normal window controls for your operating system.

Arrange Network Windows

When you work on multiple networks, you can arrange the network view windows under View → Arrange Network Windows.

Vertical

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Grid

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The Network Overview Window

The network overview window shows an overview (or "bird’s eye view") of the network. It can be used to navigate around a large network view. The blue rectangle indicates the portion of the network currently displayed in the network view window, and it can be dragged with the mouse to view other portions of the network. Zooming in will cause the rectangle to appear smaller and vice versa.

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There are 4 different ways of creating networks in Cytoscape:

1. Importing pre-existing, fixed-format network files.
2. Importing pre-existing, unformatted text or Excel files.
3. Importing data from from public databases.
4. Creating an empty network and manually adding nodes and edges.

Import Fixed-Format Network Files

Network files can be specified in any of the formats described in the Supported Network Formats section. Networks are imported into Cytoscape through the File → Import → Network menu. The network file can either be located directly on the local computer, or found on a remote computer (in which case it will be referenced with a URL).

Load Networks from Local Computer

In order to load a network from a local file you can select File → Import → Network → File... or click on on the tool bar. Choose the correct file in the file chooser dialog and press Open. Some sample network files of different types have been included in the sampleData folder in Cytoscape.

After you choose a network file, another dialog will pop up. Here, you can choose either to create a new network collection for the new network, or load the new network into an existing network collection. When you choose the latter, make sure to choose the right mapping column to map the new network to the existing network collection.

Network files in SIF, GML, and XGMML formats may also be loaded directly from the command line using the –N option.

Load Networks from a Remote Computer (URL import)

To load a network from a remote file, you can select File → Import → Network → URL.... In the import network dialog, insert the appropriate URL, either manually or using URL bookmarks. Bookmarked URLs can be accessed by clicking on the arrow to the right of the text field (see the Bookmark Manager in Preferences for more details on bookmarks). Also, you can drag and drop links from a web browser to the URL text box. Once a URL has been specified, click on the OK button to load the network.

Another issue for network import is the presence of firewalls, which can affect which files are accessible to a computer. To work around this problem, Cytoscape supports the use of proxy servers. To configure a proxy server, go to Edit → Preferences→ Proxy Settings.... This is further described in the Preferences section.

Import Networks from Unformatted Table Files

Cytoscape supports the import of networks from delimited text files and Excel workbooks using File → Import → Network → File.... An interactive GUI allows users to specify parsing options for specified files. The screen provides a preview that shows how the file will be parsed given the current configuration. As the configuration changes, the preview updates automatically. In addition to specifying how the file will be parsed, the user must also choose the columns that represent the source and target nodes as well as an optional edge interaction type.

Supported Files

The Import Network from Table function supports delimited text files and Microsoft Excel Workbooks. For Excel Workbooks with multiple sheets, one sheet can be selected for import at a time. The following is a sample table file:

source  target  interaction  boolean data       string data     floating point data
YJR022W YNR053C pp      TRUE    abcd12371       1.2344543
YER116C YDL013W pp      TRUE    abcd12372       1.2344543
YNL307C YAL038W pp      FALSE   abcd12373       1.2344543
YNL216W YCR012W pd      TRUE    abcd12374       1.2344543
YNL216W YGR254W pd      TRUE    abcd12375       1.2344543

The network table files should contain at least two columns for creating network with edges. If the file has only one column, the created network will not contain any edges. The interaction type is optional in this format. Therefore, a minimal network table looks like the following:

YJR022W YNR053C
YER116C YDL013W
YNL307C YAL038W
YNL216W YCR012W
YNL216W YGR254W

One row in a network table file represents an edge and its edge data columns. This means that a network file is considered a combination of network data and edge column data. A table may contain columns that aren't meant to be edge data. In this case, you can choose not to import those columns by clicking on the column header in the preview window. This function is useful when importing a data table like the following (1):

This data file is a tab-delimited text file and contains network data (interactions), edge data, and node data. To import network and edge data from this table, choose Unique ID A as source, Unique ID B as target, and Interactor types as interaction type. Next, turn off columns used for node data (Alternative ID A, species B, etc.). Other columns can be imported as edge data.

The network import function cannot import node table columns - only edge table columns. To import node table columns from this table, please see the Node and Edge Column Data section of this manual.

Note (1): This data is taken from the A merged human interactome datasets by Andrew Garrow, Yeyejide Adeleye and Guy Warner (Unilever, Safety and Environmental Assurance Center, 12 October 2006). Actual data files are available at http://wiki.cytoscape.org/Data_Sets/

Basic Operations

To import network from text/Excel tables, please follow these steps:

1. Select File → Import → Network → File... or click on on the tool bar.

2. Select a table file in the file chooser dialog.
3. Define the interaction parameters by specifying which columns of data contain the Source Interaction, Target Interaction, and Interaction Type. Clicking on any column header will bring up the interface for selecting source, interaction and target:

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4. (Optional) Define edge table columns, if applicable. Network table files can have edge table columns in addition to network data.

   • Enable/Disable Table Columns: You can enable/disable column data by selecting the symbol in the column editor.

     • 

   • Change Column Name and Data Types: You can also modify the column name and data type in the column editor. For more detail, see Modify Column Name/Type below.

5. Click the OK button.

Import List of Nodes Without Edges

The table import feature supports lists of nodes without edges. If you select only a source column, it creates a network without interactions. This feature is useful with the node expansion function available from some web service clients. Please read the section Importing Networks from External Database for more detail.

Advanced Options

You can select several options by clicking the Advanced Options button in the main import interface.

• Delimiter: You can select multiple delimiters for text tables. By default, Tab and Space are selected as delimiters.
• Default Interaction
• Transfer first line as column names: Selecting this option will cause all edge columns to be named according to the first data entry in that column.
• Start Import Row: Set which row of the table to begin importing data from. For example, if you want to skip the first 3 rows in the file, set 4 for this option.
• Ignore lines starting with: Rows starting with this character will not be imported. This option can be used to skip comment lines in text files.

Modify Column Name/Type

In the Import Network from Table interface, you can change the name and data type of column by clicking on any column header:

Column names and data types can be modified here.

• Modify Column Name - just enter a new column name.
• Modify Column Data Type - The following column data types are supported:
  • String
  • Boolean (True/False)
  • Integer
  • Floating Point
  • List of (one of) String/Boolean/Integer/Floating Point

Cytoscape has a basic data type detection function that automatically suggests the column data type according to its entries. This can be overridden by selecting the appropriate data type from the radio buttons provided. For lists, a global delimiter must be specified (i.e., all cells in the table must use the same delimiter).

Import Networks from Public Databases

Cytoscape has a feature called Import Network from Public Databases. Users can access various kinds of databases through this function, File → Import → Network → Public Databases....

Getting Started

To get started, select File → Import → Network → Public Databases....

Example: Retrieving Protein-Protein Interaction Networks from Multiple Databases

• Select File → Import → Network → Public Databases....

• From the pull-down menu, select the Interaction databases Universal Client.

• Enter one or more search terms, such as BRCA1.

• Click the Search button to start the search.

• Select databases from the hits. This selection will be saved as your default database list.

• Click the Import button to import selected network data.

After confirming the download of interaction data, the network of BRCA1 will be imported and visualized.

Tip: Expanding the Network: Several of the Cytoscape web services provide additional options in the node context menu. To access these options, right-click on a node and select Apps → Extend Network by public interaction database.... For example, in the screenshot, we have loaded the BRCA1 network from IntAct, and have chosen to merge this node's neighbors into the existing network.

PSICQUIC Options

PSICQUIC Web Service Client has three search modes:

• Search by ID
• Search by MIQL
• Search by Species

By default, search mode is set to Search by ID. You can search all databases by ID, such as gene symbol, Uniprot ID, or NCBI gene ID. If the search mode is set to MIQL, you can use MIQL for search. If you want to search interactions by keywords or specific functions, this is the powerful query language to filter the result. The last option is for importing all interactions for the species (i.e., interactome).

Create a New Network Manually

A new, empty network can also be created and nodes and edges manually added. To create an empty network, go to File → New → Network → Empty Network, and then manually add network components by right clicking on the network canvas or on a node.

Adding a Node

To add a new node, right-click on an empty space of the network view panel. Select Add → Node item from the pop-up menu.

Adding an Edge

To add an edge to connect nodes, right-click on the source node. Select Edit → Add Edge from the pop-up menu. Next, click on the target node. The Images below show the two steps for drawing an edge between two nodes. You can abort the drawing of the edge by pressing Esc key. You can also select two or more nodes to connect and in the right-click menu select Add → Edges Connecting Selected Nodes to create edges connecting all selected nodes.

You can delete nodes and edges by selecting a number of nodes and edges, then selecting Edit → Cut. You can also delete selected nodes and edges from the Edit menu, under Edit → Delete Selected Nodes and Edges.... You can recover any nodes and edges deleted from a network by going to Edit → Undo.

Grouping nodes

Any number of nodes can be grouped together and displayed as either one group node or as the individual nodes. To create a group, select two or more nodes and right-click to select Group → Group Selected Nodes. You will be prompted to select a name for the group node. Once a group is created, you can use the right-click menu to collapse or expand the group. You can also quickly collapse/expand a group by double-clicking on the group node or any of its children to toggle back and forth.

Collapsed group

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Expanded group

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Adding Network Annotations

Annotations in the form of text, images or shapes can be added to the network canvas by right-clicking anywhere on the canvas and selecting one of the Annotation choices in the Add menu. You can add an image of your own, choose from a shapes library or add either plain or bounded text. Shapes and text are customizable and any added annotations can be edited from the right-click context menu.

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Cytoscape has the ability to associate a Nested Network with any node. A nested network is any other network currently defined in Cytoscape. This capability allows for creation of network hierarchies as well as circular relationships. For example, various module-finding plugins make use of nested networks in the overview network that they generate. There each node representing a module contains a nested network.

Creating Nested Networks

There are currently two ways in which a user can create nested networks.

• By importing a Nested Network Format (NNF) file. (See: NNF Network Format).

• By manually constructing networks and assigning nested networks to individual nodes through the right-click node context menu. (See Nested Network Node Context Menu).

Visualization of Nested Networks

Nodes containing nested networks that are zoomed in sufficiently display an image for the nested network. If no current network view exists for the nested network the image will be a default icon, otherwise it will be a low-resolution rendering of the nested network's current layout.

Cytoscape can read network/pathway files written in the following formats:

• Simple interaction file (SIF or .sif format)
• Nested network format (NNF or .nnf format)
• Graph Markup Language (GML or .gml format)
• XGMML (extensible graph markup and modelling language).
• SBML
• BioPAX
• PSI-MI Level 1 and 2.5
• GraphML
• Delimited text
• Excel Workbook (.xls, .xlsx)

• Cytoscape.js JSON

The SIF format specifies nodes and interactions only, while other formats store additional information about network layout and allow network data exchange with a variety of other network programs and data sources. Typically, SIF files are used to import interactions when building a network for the first time, since they are easy to create in a text editor or spreadsheet. Once the interactions have been loaded and network layout has been performed, the network may be saved to GML or XGMML format for interaction with other systems. All file types listed (except Excel) are text files and you can edit and view them in a regular text editor.

SIF Format

The simple interaction format is convenient for building a graph from a list of interactions. It also makes it easy to combine different interaction sets into a larger network, or add new interactions to an existing data set. The main disadvantage is that this format does not include any layout information, forcing Cytoscape to re-compute a new layout of the network each time it is loaded.

Lines in the SIF file specify a source node, a relationship type (or edge type), and one or more target nodes:

nodeA <relationship type> nodeB
nodeC <relationship type> nodeA
nodeD <relationship type> nodeE nodeF nodeB
nodeG
...
nodeY <relationship type> nodeZ

A more specific example is:

node1 typeA node2
node2 typeB node3 node4 node5
node0

The first line identifies two nodes, called node1 and node2, and a single relationship between node1 and node2 of type typeA. The second line specifies three new nodes, node3, node4, and node5; here "node2" refers to the same node as in the first line. The second line also specifies three relationships, all of type typeB and with node2 as the source, with node3, node4, and node5 as the targets. This second form is simply shorthand for specifying multiple relationships of the same type with the same source node. The third line indicates how to specify a node that has no relationships with other nodes. This form is not needed for nodes that do have relationships, since the specification of the relationship implicitly identifies the nodes as well.

Duplicate entries are ignored. Multiple edges between the same nodes must have different edge types. For example, the following specifies two edges between the same pair of nodes, one of type xx and one of type yy:

node1 xx node2
node1 xx node2
node1 yy node2

Edges connecting a node to itself (self-edges) are also allowed:

node1 xx node1

Every node and edge in Cytoscape has a name column. For a network defined in SIF format, node names should be unique, as identically named nodes will be treated as identical nodes. The name of each node will be the name in this file by default (unless another string is mapped to display on the node using styles). This is discussed in the section on Styles. The name of each edge will be formed from the name of the source and target nodes plus the interaction type: for example, sourceName (edgeType) targetName.

The tag <edgeType> can be any string. Whole words or concatenated words may be used to define types of relationships, e.g. geneFusion, cogInference, pullsDown, activates, degrades, inactivates, inhibits, phosphorylates, upRegulates, etc.

Some common interaction types used in the Systems Biology community are as follows:

  pp .................. protein – protein interaction
  pd .................. protein -> DNA
  (e.g. transcription factor binding upstream of a regulating gene.)

Some less common interaction types used are:

  pr .................. protein -> reaction
  rc .................. reaction -> compound
  cr .................. compound -> reaction
  gl .................. genetic lethal relationship
  pm .................. protein-metabolite interaction
  mp .................. metabolite-protein interaction

Delimiters

Whitespace (space or tab) is used to delimit the names in the simple interaction file format. However, in some cases spaces are desired in a node name or edge type. The standard is that, if the file contains any tab characters, then tabs are used to delimit the fields and spaces are considered part of the name. If the file contains no tabs, then any spaces are delimiters that separate names (and names cannot contain spaces).

If your network unexpectedly contains no edges and node names that look like edge names, it probably means your file contains a stray tab that's fooling the parser. On the other hand, if your network has nodes whose names are half of a full name, then you probably meant to use tabs to separate node names with spaces.

Networks in simple interactions format are often stored in files with a .sif extension, and Cytoscape recognizes this extension when browsing a directory for files of this type.

NNF

The NNF format is a very simple format that unlike SIF allows the optional assignment of single nested network per node. No other node columns can be specified. There are only 2 possible line formats:

• A node "node" contained in a "network:"

network node

• 2 nodes linked together contained in a network:

network node1 interaction node2

If a network name (first entry on a line) appeared previously as a node name (in columns 2 or 4), the network will be nested in the node with the same name. Also, if a name that has been previously defined as a network (by being listed in the first column), later appears as a node name (in columns 2 or 4), the previously defined network will be nested in the node with the same name. In summary: any time a name is used as both, a network name , and a node name, this implies that the network will be nested in the node of the same name. Additionally comments may be included on all lines. Comments start with a hash mark '#' and continue to the end of a line. Trailing comments (after data lines) and entirely blank lines anywhere are also permissible. Please note that if you load multiple NNF files in Cytoscape they will be treated like a single, long concatenated NNF file! If you need to embed spaces, tabs or backslashes in a name, you must escape it by preceding it with a backslash, so that, e.g. an embedded backslash becomes two backslashes, an embedded space a backslash followed by a space etc.

Examples

Example 1

Example_1      C
Example_1      network1
network1       A        pp        B
network1       B        pp        A
Example_1      C        pp        B

Example 2

Example_2      M1
Example_2      M2
M1             A
M2             B        pp        C
Example_2      A        pp        B
Example_2      M1       im        M2

Example 3

Example_3      M1       im        M2
Example_3      M3       im        M1
Example_3      M2       im        M3
Example_3      C        pp        M3
Example_3      M2       pp        C
M1             A
M2             A        pp        B
M3             B        pp        C

==== Example 4 ==== Example_4 M1*/ /* root M3*/ /* M1 A pp B M1 B pp A Example_4 C pp B M3 M2 M2 D M3 E pp F M3 D pp F M3 D pp E Example_4 D pp C Example_4 A pp M2*/ /* Example_4 B pp M3 Example_4 M2 pp B

Example 5

Example_5      M4
M4             D
M4             M3
M3             M2        pp        C
M2             M1        pp        B
M1             A
M4             C         pp        D

GML Format

In contrast to SIF, GML is a rich graph format language supported by many other network visualization packages. The GML file format specification is available at:

http://www.infosun.fmi.uni-passau.de/Graphlet/GML/

It is generally not necessary to modify the content of a GML file directly. Once a network is built in SIF format and then laid out, the layout is preserved by saving to and loading from GML. Properties specified in a GML file will result in a new style named Filename.style when that GML file is loaded.

XGMML Format

XGMML is the XML evolution of GML and is based on the GML definition. In addition to network data, XGMML contains node/edge/network column data. The XGMML file format specification is available at:

http://cgi5.cs.rpi.edu/research/groups/pb/punin/public_html/XGMML/

XGMML is now preferred to GML because it offers the flexibility associated with all XML document types. If you're unsure about which to use, choose XGMML.

There is a java system property "cytoscape.xgmml.repair.bare.ampersands" that can be set to "true" if you have experience trouble reading older files.

This should only be used when an XGMML file or session cannot be read due improperly encoded ampersands, as it slows down the reading process, but this is still preferable to attempting to fix such files using manual editing.

SBML (Systems Biology Markup Language) Format

The Systems Biology Markup Language (SBML) is an XML format to describe biochemical networks. SBML file format specification is available at:

http://sbml.org/documents/

BioPAX (Biological PAthways eXchange) Format

BioPAX is an OWL (Web Ontology Language) document designed to exchange biological pathways data. The complete set of documents for this format is available at:

http://www.biopax.org/

PSI-MI Format

The PSI-MI format is a data exchange format for protein-protein interactions. It is an XML format used to describe PPI and associated data. PSI-MI XML format specification is available at:

http://psidev.sourceforge.net/mi/xml/doc/user/

GraphML

GraphML is a comprehensive and easy-to-use file format for graphs. It is based on XML. The complete set of documents for this format is available at:

http://graphml.graphdrawing.org/

Delimited Text Table and Excel Workbook

Cytoscape has native support for Microsoft Excel files (.xls, .xlsx) and delimited text files. The tables in these files can have network data and edge columns. Users can specify columns containg source nodes, target nodes, interaction types, and edge columns during file import. Some of the other network analysis tools, such as igraph (http://cneurocvs.rmki.kfki.hu/igraph/), has feature to export graph as simple text files. Cytoscape can read these text files and build networks from them. For more detail, please read the Import Free-Format Tables section of the Creating Networks section.

Cytoscape.js JSON

From Cytoscape 3.1.0 on, Cytoscape supports Cytoscape.js JSON files. You can use this feature to export your network visualizations to web browsers. Cytoscape.js has two ways to represent network data, and currently both reader and writer support only the array style graph notation. For example, this network in Cytoscape:

will be exported to this JSON:

{
  "elements" : {
    "nodes" : [ {
      "data" : {
        "id" : "723",
        "selected" : false,
        "annotation_Taxon" : "Saccharomyces cerevisiae",
        "alias" : [ "RPL31A", "RPL34", "S000002233", "ribosomal protein L31A (L34A) (YL28)" ],
        "shared_name" : "YDL075W",
        "SUID" : 723,
        "degree_layout" : 1,
        "name" : "YDL075W"
      },
      "position" : {
        "x" : 693.0518315633137,
        "y" : -49.47506554921466
      },
      "selected" : false
    }, {
      "data" : {
        "id" : "726",
        "selected" : false,
        "annotation_Taxon" : "Saccharomyces cerevisiae",
        "alias" : [ "RP23", "RPL16B", "S000005013", "ribosomal protein L16B (L21B) (rp23) (YL15)" ],
        "shared_name" : "YNL069C",
        "SUID" : 726,
        "degree_layout" : 1,
        "name" : "YNL069C"
      },
      "position" : {
        "x" : 627.3147710164387,
        "y" : -205.99251969655353
      },
      "selected" : false
    }, {
      "data" : {
        "id" : "658",
        "selected" : false,
        "annotation_Taxon" : "Saccharomyces cerevisiae",
        "alias" : [ "RPL11B", "S000003317", "ribosomal protein L11B (L16B) (rp39B) (YL22)" ],
        "shared_name" : "YGR085C",
        "SUID" : 658,
        "degree_layout" : 2,
        "name" : "YGR085C"
      },
      "position" : {
        "x" : 804.3092778523762,
        "y" : -245.6235926946004
      },
      "selected" : false
    }, {
      "data" : {
        "id" : "660",
        "selected" : false,
        "annotation_Taxon" : "Saccharomyces cerevisiae",
        "alias" : [ "KAP108", "S000002803", "SXM1" ],
        "shared_name" : "YDR395W",
        "SUID" : 660,
        "degree_layout" : 8,
        "name" : "YDR395W"
      },
      "position" : {
        "x" : 730.8733342488606,
        "y" : -157.50702317555744
      },
      "selected" : false
    }, {
      "data" : {
        "id" : "579",
        "selected" : false,
        "annotation_Taxon" : "Saccharomyces cerevisiae",
        "alias" : [ "RPL11A", "S000006306", "ribosomal protein L11A (L16A) (rp39A) (YL22)" ],
        "shared_name" : "YPR102C",
        "SUID" : 579,
        "degree_layout" : 2,
        "name" : "YPR102C"
      },
      "position" : {
        "x" : 841.1395696004231,
        "y" : -130.77909119923908
      },
      "selected" : false
    }, {
      "data" : {
        "id" : "578",
        "selected" : false,
        "annotation_Taxon" : "Saccharomyces cerevisiae",
        "alias" : [ "GRC5", "QSR1", "RPL10", "S000004065", "ribosomal protein L10" ],
        "shared_name" : "YLR075W",
        "SUID" : 578,
        "degree_layout" : 2,
        "name" : "YLR075W"
      },
      "position" : {
        "x" : 910.3755162556965,
        "y" : -217.0562556584676
      },
      "selected" : false
    } ],
    "edges" : [ {
      "data" : {
        "id" : "659",
        "source" : "658",
        "target" : "578",
        "selected" : false,
        "interaction" : "pp",
        "shared_interaction" : "pp",
        "shared_name" : "YGR085C (pp) YLR075W",
        "SUID" : 659,
        "name" : "YGR085C (pp) YLR075W"
      },
      "selected" : false
    }, {
      "data" : {
        "id" : "661",
        "source" : "658",
        "target" : "660",
        "selected" : false,
        "interaction" : "pp",
        "shared_interaction" : "pp",
        "shared_name" : "YGR085C (pp) YDR395W",
        "SUID" : 661,
        "name" : "YGR085C (pp) YDR395W"
      },
      "selected" : false
    }, {
      "data" : {
        "id" : "724",
        "source" : "660",
        "target" : "723",
        "selected" : false,
        "interaction" : "pp",
        "shared_interaction" : "pp",
        "shared_name" : "YDR395W (pp) YDL075W",
        "SUID" : 724,
        "name" : "YDR395W (pp) YDL075W"
      },
      "selected" : false
    }, {
      "data" : {
        "id" : "733",
        "source" : "660",
        "target" : "579",
        "selected" : false,
        "interaction" : "pp",
        "shared_interaction" : "pp",
        "shared_name" : "YDR395W (pp) YPR102C",
        "SUID" : 733,
        "name" : "YDR395W (pp) YPR102C"
      },
      "selected" : false
    }, {
      "data" : {
        "id" : "727",
        "source" : "660",
        "target" : "726",
        "selected" : false,
        "interaction" : "pp",
        "shared_interaction" : "pp",
        "shared_name" : "YDR395W (pp) YNL069C",
        "SUID" : 727,
        "name" : "YDR395W (pp) YNL069C"
      },
      "selected" : false
    }, {
      "data" : {
        "id" : "580",
        "source" : "578",
        "target" : "579",
        "selected" : false,
        "interaction" : "pp",
        "shared_interaction" : "pp",
        "shared_name" : "YLR075W (pp) YPR102C",
        "SUID" : 580,
        "name" : "YLR075W (pp) YPR102C"
      },
      "selected" : false
    } ]
  }
}

And this is a sample visualization in Cytoscape.js:

Important Note

Export network and table to Cytoscape.js feature in Cytoscape creates a JSON file WITHOUT style. This means that you need to export the style in a separate JSON file if you apply style to your network. Please read Style section for more details.

Interaction networks are useful as stand-alone models. However, they are most powerful for answering scientific questions when integrated with additional information. Cytoscape allows the user to add arbitrary node, edge and network information to Cytoscape as node/edge/network data columns. This could include, for example, annotation data on a gene or confidence values in a protein-protein interaction. These column data can then be visualized in a user-defined way by setting up a mapping from columns to network properties (colors, shapes, and so on). The section on Styles discusses this in greater detail.

Import Data Table Files

Cytoscape offers support for importing data from delimited text and MS Excel data tables.

Sample Data Table 1

The data table file should contain a primary key column and at least one data column. The maximum number of data columns is unlimited. The Alias column is an optional feature, as is using the first row of data as column names. Alternatively, you can specify each column name from the File → Import → Table → File... user interface.

Basic Operation

• 

1. Select File → Import → Table → File....

2. Select a data file. The file can be either a text or Excel (.xls/.xlsx) file.

3. In the Target Table Data section, choose where to import the data to. You can choose an existing network collection, a specific network only, or you can choose to import the data to an Unassigned Table (described below).

4. Depending on what you choose in the Where to import Table Data drop-down, you will need to select a network collection or specific network. You will also need to select Importing Type, that is whether the data is node, edge or network table columns.

5. If the table is not properly delimited in the preview panel, change the delimiter in the Advanced Options panel. The default delimiter is tab. This step is not necessary for Excel Workbooks.

6. By default, the first column is designated as the primary key. Change the key column if necessary.

7. Click OK to import.

Unassigned Table

As of Cytoscape 3.1. it is possible to import data tables without assigning them to existing networks, meaning the data doesn't have to correspond to any nodes/edges currently loaded. If a data table is imported as unassigned and a network is later imported that maps to the data in terms of nodes or edges, the data will link automatically. This is useful when loading a large dataset (for example expression data), defining a Style for visualizing the data on networks and later loading individual networks to view the data, for example from an online database. This feature allows the data to be automatically linked to any network that is applicable, without having to load the data for each network.

Legacy Cytoscape Attributes Format

In addition to tabular data, the simple attribute file format used in previous versions of Cytoscape is still supported. Node and edge data files are simply formatted: a node data file begins with the name of the column on the first line (note that it cannot contain spaces). Each following line contains the name of the node, followed by an equals sign and the data value. Numbers and text strings are the most common data types. All values for a given column must have the same type. For example:

FunctionalCategory
YAL001C = metabolism
YAR002W = apoptosis
YBL007C = ribosome

An edge data file has much the same structure, except that the name of the edge is the source node name, followed by the interaction type in parentheses, followed by the target node name. Directionality counts, so switching the source and target will refer to a different (or perhaps non-existent) edge. The following is an example edge data file:

InteractionStrength
YAL001C (pp) YBR043W = 0.82
YMR022W (pd) YDL112C = 0.441
YDL112C (pd) YMR022W = 0.9013

Since Cytoscape treats edge data as directional, the second and third edge data values refer to two different edges (source and target are reversed, though the nodes involved are the same).

Each data column is stored in a separate file. Node and edge data files use the same format, and have the suffix ".attrs".

Node and edge data may be loaded via the File → Import → Table menu, just as data table files are.

When expression data is loaded using an expression matrix, it is automatically loaded as node data unless explicitly specified otherwise.

Node and edge data columns are attached to nodes and edges, and so are independent of networks. Data values for a given node or edge will be applied to all copies of that node or edge in all loaded network files, regardless of whether the data file or network file is imported first.

Detailed file format (Advanced users)

Every data file has one header line that gives the name of the data column, and optionally some additional meta-information about that data column. The format is as follows:

columnName (class=JavaClassName)

The first field is always the column name: it cannot contain spaces. If present, the class field defines the name of the class of the data values. For example, java.lang.String or String for Strings, java.lang.Double or Double for floating point values, java.lang.Integer or Integer for integer values, etc. If the value is actually a list of values, the class should be the type of the objects in the list. If no class is specified in the header line, Cytoscape will attempt to guess the type from the first value. If the first value contains numbers in a floating point format, Cytoscape will assume java.lang.Double; if the first value contains only numbers with no decimal point, Cytoscape will assume java.lang.Integer; otherwise Cytoscape will assume java.lang.String. Note that the first value can lead Cytoscape astray: for example,

floatingPointDataColumn
firstName = 1
secondName = 2.5

In this case, the first value will make Cytoscape think the values should be integers, when in fact they should be floating point numbers. It's safest to explicitly specify the value type to prevent confusion. A better format would be:

floatingPointDataColumn (class=Double)
firstName = 1
secondName = 2.5

or

floatingPointDataColumn 
firstName = 1.0
secondName = 2.5

Every line past the first line identifies the name of an object (a node in a node data file or an edge in a edge data file) along with the String representation of the data value. The delimiter is always an equals sign; whitespace (spaces and/or tabs) before and after the equals sign is ignored. This means that your names and values can contain whitespace, but object names cannot contain an equals sign and no guarantees are made concerning leading or trailing whitespace. Object names must be the Node ID or Edge ID as seen in the left-most column of the Table Panel if the data column is to map to anything. These names must be reproduced exactly, including case, or they will not match.

Edge names are all of the form:

sourceName (edgeType) targetName

Specifically, that is

Note that tabs are not allowed in edge names. Tabs can be used to separate the edge name from the "=" delimiter, but not within the edge name itself. Also note that this format is different from the specification of interactions in the SIF file format. To be explicit: a SIF entry for the previous interaction would look like

sourceName edgeType targetName

or

To specify lists of values, use the following syntax:

listDataColumnName (class=java.lang.String)
firstObjectName = (firstValue::secondValue::thirdValue)
secondObjectName = (onlyOneValue)

This example shows a data column whose value is defined as a list of text strings. The first object has three strings, and thus three elements in its list, while the second object has a list with only one element. In the case of a list every data value uses list syntax (i.e. parentheses), and each element is of the same class. Again, the class will be inferred if it is not specified in the header line. Lists are not supported by Styles and so can’t be mapped to network properties.

Newline Feature

Sometimes it is desirable to for data values to include linebreaks, such as node labels that extend over two lines. You can accomplish by inserting \n into the data value. For example:

newlineDataColumn
YJL157C = This is a long\nline for a label.

Table Panel

When Cytoscape is started, the Table Panel appears in the bottom right of the main Cytoscape window. This browser can be hidden and restored using the F5 key or the View → Show/Hide Table Panel menu option. Like other Panels, the browser can be undocked by pressing the little icon in the top right corner.

To swap between displaying node, edge, and network Data Tables use the tabs on the bottom of the Table Panel. By default, the Table Panel displays columns for all nodes and edges in the selected network. To display columns for only selected nodes/edges, click the Change Table Mode button at the top left. To change the columns that are displayed, click the Show Column button and choose the columns that are to be displayed (select various columns by clicking on them, and then click elsewhere on the screen to close the column list).

Most column values can be edited by double-clicking the cell (only the ID cannot be edited). Newline characters can be inserted into String columns either by pressing Enter or by typing "\n". Once finished editing, click outside of the editing cell in the Table Panel or press Shift-Enter to save your edits. Pressing Esc while editing will undo any changes.

Rows in the panel can be sorted alphabetically by specific column by clicking on a column heading. A new column can be created using the Create New column button, and must be one of four types – integer, string, real number (floating point), or boolean. Columns can be deleted using the Delete Columns... button. NOTE: Deleting columns removes them from Cytoscape, not just the Table Panel! To remove columns from the panel without deleting them, simply unselect the column using the Select Columns button.

Import Data Table from Public Databases

It is also possible to import node data columns from public databases via web services, for example from BioMart.

Basic Operation

1. Load a network, for example galFiltered.sif.

2. Select File → Import → Table → Public Databases....

3. You will first be asked to select from a set of web services. For this example, we will choose ENSEMBL GENES 73 (SANGER UK).

1. In the Import Data Table from Web Services dialog, select a Data Source. Since galFiltered.sif is a yeast network, select ENSEMBL GENES - SACCHAROMYCES CEREVISIAE.

2. For Key Column in Cytoscape, select shared name for Column and Ensembl Gene ID for Data Type.

The type of identifier selected under Data Type must match what is used in the selected Column in the network.

1. Select the data columns you want to import.

2. Select Import.

When import is complete, you can see the newly imported data columns in the Table Panel.

Annotations in Cytoscape are stored as a set of ontologies (e.g. the Gene Ontology, or GO). An ontology consists of a set of controlled vocabulary terms that annotate the objects. For example, using the Gene Ontology, the Saccharomyces Cerevisiae CDC55 gene has a biological process described as “protein biosynthesis”, to which GO has assigned the number 6412 (a GO ID).

GO 8150 biological_process

• GO 7582 physiological processes
  • GO 8152 metabolism
    • GO 44238 primary metabolism
      • GO 19538 protein metabolism
        • GO 6412 protein biosynthesis

Graphical View of GO Term 6412: protein biosynthesis

Cytoscape can use this ontology DAG (Directed Acyclic Graph) to annotate objects in networks. The Ontology Server (originally called "BioDataServer") is a Cytoscape feature which allows you to load, navigate, and assign annotation terms to nodes and edges in a network. Cytoscape 2.4 now has an enhanced GUI for loading ontology and associated annotation, enabling you to load both local and remote files.

Ontology and Annotation File Format

The standard file formats used in the Cytoscape Ontology Server are OBO and Gene Association. The GO website details these file formats:

Ontologies and Definitions: http://www.geneontology.org/GO.downloads.shtml#ont

Current Annotations: http://www.geneontology.org/GO.current.annotations.shtml

Default List of Ontologies

Cytoscape provides a list of ontologies available in OBO format. If an Internet connection is available, Cytoscape will import ontology and annotation files directly from the remote source. The table below lists the included ontologies.

Although Cytoscape can import all kinds of ontologies in OBO format, annotation files are associated with specific ontologies. Therefore, you need to provide the correct ontology-specific annotation file to annotate nodes/edges/networks in Cytoscape. For example, while you can annotate human network data using the GO Full ontology with human Gene Association files, you cannot use a combination of the human Disease Ontology file and human Gene Association files, because the Gene Association file is only compatible with GO.

Gene Association File

The Gene Association files provide annotation only for the Gene Ontology. It is a species-specific annotation file for GO terms. Gene Association files will only work with Gene Ontology annotation.

Sample Gene Association File (gene_association.sgd - annotation file for yeast):

Import Ontology and Annotation

Cytoscape provides a graphical user interface to import both ontology and annotation files at the same time.

Note: All data sources in the preset list are remote URLs, meaning a network connection is required.

• Select File → Import → Ontology and Annotation... to open the "Import Ontology and Annotation" interface. From the Annotation drop-down list, select a gene association file for your network. For example, if you want to annotate the yeast network, select "Gene Association file for Saccharomyces cerevisiae".

* Select an Ontology data (OBO file) from the Ontology drop-down list. If the file is not loaded yet, it will be shown in red. The first three files are Gene Ontology files. You can load other ontologies, but you need your own annotation file to annotate networks.

Once you click the Import button, Cytoscape will start loading OBO and Gene Association files from the remote sources. If you choose GO Full it may take a while since it is a large data file.

• When Cytoscape finishes importing files, the import window will be automatically closed. All columns mapped by this function have the prefix "annotation" and look like this: annotation.[column_name].

Note: Cytoscape supports both OBO formats: version 1.0 and 1.2.

Column Formulas

Introduction

Column data values may be formulas. A typical example is =ABS($otherColumn + LOG(10.2)). Formulas are modeled after Excel™ but only support references to other columns at the same node, edge or network. Since Cytoscape column names may contain embedded spaces, optional braces around the column name (required if the name is not simply a letter followed by one or more letters or digits) is allowed e.g. ${a name with spaces}. Backslashes, opening braces and dollar signs in column names have to be escaped with a leading backslash. For example the column name ex$am{p\le would have to be written as ${ex\$am\{p\\le}. Finally, column names are case sensitive.

String constants are written with double-quotes ". In order to embed a double-quote or a backslash in a string they have to be escaped with a leading backslash, therefore the string "\ must be written as "\"\\". Formula results must be compatible with the type of the column that they have been assigned to. The rules are rather lax though, for example anything can be interpreted as a string and all numeric values will be accepted for a boolean (or logical) column data where non-zero will be interpreted as true and zero as false. For integer columns, floating point values will be converted using the rules of the Excel™ INT function. Parentheses can be used for grouping and to change evaluation order. The operator precedence rules follow those of standard arithmetic.

Operators

Currently supported operators are the four basic arithmetic operators and the ^ exponentiation operator. +, -, *, and \ are left-associative and ^ is right-associative. The string concatenation operator is &. Supported boolean or logical operators are the comparison operators <, >, <=, >=, =, and <> (not equal).

Supported Functions

Currently we support the following functions:

Numeric Functions

• Abs -- Returns the absolute value of a number.
• ACos -- Returns the arccosine of a number.
• ASin -- Returns the arcsine of a number.
• ATan2 -- Returns the arctangent of two numbers x and y.
• Average -- Returns the average of a group of numbers.
• Cos -- Returns the cosine of an angle given in radians.
• Cosh -- Returns the hyperbolic sine of its argument.
• Count -- Returns the number of numeric values in a list.
• Degrees -- Returns its argument converted from radians to degrees.
• Exp -- Returns e raised to a specified number.
• Ln -- Returns the natural logarithm of a number.
• Log -- Returns the logarithm of a number to a specified base.
• Max -- Returns the maximum of a group of numbers.
• Median -- Returns the median of a list of numbers.
• Min -- Returns the minimum of a group of numbers.
• Mod -- Calculates the modulus of a number.
• Pi -- Returns an approximation of the value of π.
• Radians -- Returns its argument converted from degrees to radians.
• Round -- Rounds a number to a specified number of decimal places.
• Sin -- Returns the sine of an angle given in radians.
• Sinh -- Returns the hyperbolic sine of its argument.
• Sqrt -- Calculates the square root of a number.
• Tan -- returns the tangent of its argument in radians.
• Tanh -- returns the hyperbolic tangent of its argument in radians.
• Trunc -- Truncates a number.

String Functions

• Concatenate -- Concatenates two or more pieces of text.
• Left -- Returns a prefix of s string.
• Len -- Returns the length of a string.
• Lower -- Converts a string to lowercase.
• Mid -- Selects a substring of some text.
• Right -- Returns a suffix of a string.
• Substitute -- Replaces some text with other text.

• Text -- Format a number using the Java DecimalFormat class' conventions.

• Upper -- Converts a string to uppercase.
• Value -- Converts a string to a number.

Logical/Boolean Functions

• And -- Returns the logical conjunction of any number of boolean values.
• Not -- Returns the logical negation of a boolean value.
• Or -- Returns the logical disjunction of any number of boolean values.

List Functions

• First -- Returns the first entry in a list.
• Last -- Returns the last entry in a list.
• Nth -- Returns the n-th entry in a list.

Statistical Functions

• Largest -- the kth largest value in a list.

• GeoMean -- the geometric mean of a set of numbers.

• HarMean -- the harmonic mean of a set of numbers.

• Mode -- the mode of a set of numbers.

• NormDist -- Returns the pdf or CDF of the normal distribution.

• Permut -- Returns the number of permutations for a given number of objects.

• StDev - sample standard deviation.

• Var -- sample variance.

Miscellaneous Functions

• Combin - Returns the number of combinations for a given number of objects.
• If -- Returns one of two alternatives based on a boolean value.

• ListToString -- Returns a string representation of a list.

• Now -- Returns a string representation of the current date and time.
• Today -- returns a string representation of the current date.

Pitfalls

The possibly biggest problem is the referencing of other columns that have null values. This is not allowed and leads to errors. In order to mitigate this problem we support the following optional syntax for column references: ${columnName:defaultValue}. The interpretation is that if columnName is null, then the default value will be used, otherwise the value of the referenced value will be used instead. The referenced column must still be a defined column and not an arbitrary name! The other potential problem is when there are circular column reference dependencies. Circular dependencies will be detected at formula evaluation time and lead to a run-time error.

The Formula Builder

In order to ease the creation of formulas as well as to facilitate discovery of built-in functions we provide a Function Builder in the Table Panel. After selecting a non-list column cell, you can invoke it by clicking on . This should bring up the Function Builder which looks like this:

Select a function on the left hand side of the dialog - here, we've selected the ABS function. Next to the list of functions, you can specify one or more arguments. This can either be a column (selected from the drop-down list) or a constant specified in the box below. If you select a column, the value of that column (in the row containing the formula) will be used, and the function result will be updated dynamically when that value changes. Click Add to add an argument - you can add one or more depending on how many arguments the function accepts. At the bottom of the dialog is a preview of the current formula. Under Apply to, you can select whether the formula will apply to the current cell only, the cell selection, or the entire column. Click OK when you are satisfied with the result, or Cancel to discard any changes.

The Function Builder is a useful tool for discovery of the list of built-in functions, which has the return type matching the data type of the column. Arguments can either be selected from a list of named columns, or constant values can be entered in a text entry field. A major shortcoming at this time is that the Formula Builder won't let you compose functions with function calls as arguments. If you need the most general functionality, please type the expression directly into a cell.

A Note for App Writers

It is relatively easy to add your own built-in formula functions. A simple function can probably be implemented in 15 to 20 minutes. It can then be registered via the parser and becomes immediately available to the user. It will of course also show up in the drop-down list in the Function Builder.

Search Bar

You can search for nodes and edges by column value directly through Cytoscape's tool bar. For example, to select nodes or edges with a column value that starts with "STE", type ste* in the search bar. The search is case-insensitive. The * is a wildcard character that matches zero or more characters, while "?" matches exactly one character. So ste? would match "STE2" but would not match "STE12". Searching for ste* would match both.

To search a specific column, you can prefix your search term with the column name followed by a :. For example, to select nodes and edges that have a "COMMON" column value that starts with "STE", use common:ste*. If you don't specify a particular column, all columns will be searched.

Columns with names that contain spaces, quotes, or characters other than letters and numbers currently do not work when searching a specific column. This will be fixed in a future release.

To search for column values that contain special characters you need to escape those characters using a "\". For example, to search for "GO:1232", use the query GO\:1232. The complete list of special characters is:

+ - & | ! ( ) { } [ ] ^ " ~ * ? : \

Note: Escaping characters only works when searching all columns. It currently does not work for column-specific searching. This will be fixed in a future release.

Filters

Cytoscape 3 provides a new user interface for filtering nodes and edges. These tools can be found in the Select panel:

There are two types of filters. On the Filter tab are narrowing filters, which can be combined into a tree. On the Chain tab are chainable filters, which can be combined in a linear chain.

Narrowing Filters

Narrowing filters are applied to the entire network, and are used to select a subset of nodes or edges in a network based on user-specified constraints. For example, you can find edges with a weight between 0 and 5.5, or nodes with degree less than 3. A filter can contain an arbitrary number of sub-filters.

To add a filter click on the "+" button. To delete a filter (and all its sub-filters) click the "x" button. To move a filter grab the handle with the mouse and drag and drop the filter on its intended destination. Dropping a filter on top of another filter will group the filters into a composite filter.

Interactive Filter Application Mode

Due to the nature of narrowing filters, Cytoscape can apply them to a network efficiently and interactively. Some filters even provide slider controls to quickly explore different thresholds. This is the default behavior on smaller networks. For larger networks, Cytoscape automatically disables this interactivity. You can override this by manually checking the Apply Automatically box above the Apply button:

Cytoscape comes packaged with the following narrowing filters:

Column Filter

This filter will match nodes or edges that have particular column values. For numeric columns sliders are provided to set minimum and maximum values, or the values may be entered manually.

From string columns, a variety of matching options are provided:

For example, column values can be checked to see if they contain or match exactly the text entered in the text box. More complex matching criteria can be specified by using a Java-style regular expression.

By default string matching is case insensitive. Case sensitive matching requires the use of a regular expression that starts with "(?-i)". For example to match the text "ABC" in a case sensitive way use the following regular expression: "(?-i)ABC".

Cytoscape uses Java regular expression syntax.

Degree Filter

The degree filter matches nodes with a degree that falls within the given minimum and maximum values, inclusive. You can choose whether the filter operates on the in-degree, out-degree or overall (in + out) degree.

Topology Filter

The topology filter matches nodes having a certain number of neighbors which are within a fixed distance away, and which match a sub-filter. The thresholds for the neighborhood size and distance can be set independently, and the sub-filter is applied to each such neighbor node.

The topology filter will successfully match a node if the sub-filter matches against the required number of neighbor nodes.

Grouping and Organizing Filters

By default, nodes and edges need to satisfy the constraints of all your filters. You can change this so that instead, only the constraints of at least one filter needs to be met in order to match a node or edge. This behavior is controlled by the Match all/any drop-down box. This appears once your filter has more than one sub-filter. For example, suppose you wanted to match nodes with column COMMON containing ste or cdc, but you only want nodes with degree 5 or more, you'd first construct a filter that looks like this:

This filter will match nodes where COMMON contains ste and cdc. To change this to a logical or operation, drag either of the column filters by its handle onto the other column filter to create a new group. Now change the group's matching behavior to Match any:

You can also reorder filters by dropping them in-between existing filters.

Chainable Filters

Chainable filters are combined in an ordered list. The nodes and edges in the output of a filter become the input of the next filter in the chain. The first filter in the chain gets its input from the current selection or from a filter on the Filter tab. The output of the last filter becomes the new selection.

You can specify the input to the first filter in the chain by selecting a Start with, where Current selection refers to the nodes and edges currently selected. You can also choose a narrowing filter, which produces a different set of selected nodes and edges.

Chainable filters can be reordered by dragging one by the handle and dropping it between existing filters.

Cytoscape currently bundles the following chainable filters:

Edge Interaction Transformer

This transformer will go through all the input edges and selectively add their source nodes, target nodes, or both, to the output. This is useful for adding nodes that are connected to edges that match a particular filter.

Output options:

• Add (default): Automatically includes all input nodes and edges in the output, and adds source or target nodes from input edges to the output.
• Replace with: Does not automatically include input nodes and edges in the output. Only outputs nodes that match the filter.

A sub-filter may be added as well. When a sub-filter is present the source/target nodes must match the filter to be included in the output.

Node Adjacency Transformer

This transformer is used to add nodes and edges that are adjacent to the input nodes. A sub-filter may be specified as well.

Note that pressing the Apply button repeatedly may cause the selection to continuously expand. This allows adjacent nodes that are at greater distances to be added.

Output options:

• Add (default): Automatically includes all input nodes and edges in the output, and adds selected adjacent nodes and edges.
• Replace with: Only outputs the adjacent nodes/edges.

Select options:

• Adjacent nodes: Output nodes that are adjacent to the input nodes.
• Adjacent edges: Output edges that are adjacent (incident) to the input nodes.
• Adjacent nodes and edges (default): Output both nodes and edges that are adjacent to the input nodes.

Edge direction options. (Hidden by default, click the small arrow icon to reveal.):

• Incoming: Only include adjacent nodes/edges when the adjacent edge is incoming.
• Outgoing: Only include adjacent nodes/edges when the adjacent edge is outgoing.
• Incoming and Outgoing (default): Ignore the directionality of adjacent edges.

Sub-filter options. (Available when a sub-filter has been added.):

• Adjacent nodes (default): The sub-filter is only applied to adjacent nodes. (Edges to the adjacent nodes are still included in the output.)
• Adjacent edges: The sub-filter is only applied to adjacent edges. (Nodes connected to the adjacent edges are still included in the output.)
• Adjacent nodes and edges: Both the adjacent edge and its connected node must match the filter. Note that for a filter to match an edge and a node at the same time it should be a compound filter that is set to "Match any (OR)".

Working with Narrowing and Chainable Filters

The name of active filter appears in the drop-down box at the top of Select panel. Beside this is the options button which will allow you to rename, remove or export the active filter. It also lets you create a new filter, or import filters.

At the bottom of the Select panel, there is an Apply button that will re-apply the active filter. On the opposite side of the progress bar is the cancel button, which will let you interrupt a long-running filter.

The Select Menu

The Select → Nodes and Select → Edges menus provide several mechanisms for selecting nodes and edges. Most options are fairly straightforward; however, some need extra explanation.

Select → Nodes → From ID List File... selects nodes based on node identifiers found in a specified file. The file format is simply one node id per line:

Node1
Node2
Node3
...

Basic Network Navigation

Cytoscape uses a Zoomable User Interface for navigating and viewing networks. ZUIs use two mechanisms for navigation: zooming and panning. Zooming increases or decreases the magnification of a view based on how much or how little a user wants to see. Panning allows users to move the focus of a screen to different parts of a view.

Zoom

Cytoscape provides two mechanisms for zooming: toolbar buttons and the scroll wheel. Use the zooming buttons located on the toolbar to zoom in and out of the interaction network shown in the current network display. Zoom icons are detailed below:

From Left to Right:

• Zoom In
• Zoom Out
• Zoom Out to Display all of Current Network
• Zoom Selected Region

Using the scroll wheel, you can zoom in by scrolling up and zoom out by scrolling downwards. These directions are reversed on Macs with natural scrolling enabled (the default for Mac OS X Lion and newer versions).

Pan

There are several ways to pan the network:

• Middle Click and Drag - You can pan the network image by holding down the middle mouse button and moving the mouse.
• Command Key + Drag (Mac only) - If you use Mac without middle button, you can pan the view by holding down Command key and then drag.

• Dragging Box on Network Overview - You can also pan the image by holding down the left mouse button over the blue box in the overview panel in the lower part of the Network tab in the Control Panel.

Other Mouse Behaviors

Select

Click the left mouse button on a node or edge to select that object. You can hold down the Shift key (or Ctrl key on PCs) to select more than one node/edge or you can hold down the left mouse button and drag the mouse to select groups of nodes/edges.

Context

Click the right mouse button (or Ctrl+left mouse button on Macs) on a node/edge to launch a context-sensitive menu with additional information about the node/edge.

Node Context Menu

This menu can change based on the current context. For nodes, it typically shows:

• Add
• Edit
• Select
• Group
• Nested Networks
• Apps
• External Links
• Preferences

Edges usually have the following menu:

• Edit
• Select
• Apps
• External Links
• Preferences

Apps can contribute their own items into node and edge context menus. These additions usually appear in the Apps section of the context menu.

Nested Network Node Context Menu

• Add Nested Network: Lets the user select any network in Cytoscape as the current node's nested network. If the current node already has a nested network it will be replaced.

• Remove Nested Network: Removes the currently associated nested network from a node. The associated network is not deleted. Only the association between the node and the network is removed.

• Go to Nested Network: The current node's nested network will be the current network view and have the focus. Should a network view for the nested network not exist, it will be created.

More information about nested networks can be found in the Nested Networks section.

Automatic Layout Algorithms

The Layout menu has an array of features for organizing the network visually according to one of several algorithms, aligning and rotating groups of nodes, and adjusting the size of the network. Cytoscape layouts have three different sources, which are reflected in the Layout menu.

With the exception of the yFiles layouts (explained below), Cytoscape Layouts have the option to operate on only the selected nodes, and all provide a Settings... panel to change the parameters of the algorithm. Most of the Cytoscape layouts also partition the graph before performing the layout. In addition, many of these layouts include the option to take either node or edge columns into account. A few of the layout algorithms are:

Grid Layout

• 

The grid layout is a simple layout the arranges all of the nodes in a square grid. This is the default layout and is always available as part of the Cytoscape core. It is available by selecting Layout → Grid Layout. A sample screen shot is shown above.

Edge-weighted Spring-Embedded Layout

• 

The spring-embedded layout is based on a “force-directed” paradigm as implemented by Kamada and Kawai (1988). Network nodes are treated like physical objects that repel each other, such as electrons. The connections between nodes are treated like metal springs attached to the pair of nodes. These springs repel or attract their end points according to a force function. The layout algorithm sets the positions of the nodes in a way that minimizes the sum of forces in the network. This algorithm can be applied to the entire network or a portion of it by selecting the appropriate options from Layout → Edge-weighted Spring Embedded.

Attribute Circle Layout

• 

The Attribute Circle layout is a quick, useful layout, particularly for small networks, that will locate all of the nodes in the network around a circle. The node order is determined by a user-selected node column. The result is that all nodes with the same value for that column are located together around the circle. Using Layout → Attribute Circle Layout → column to put all nodes around a circle using column to position them. The sample screen shot above shows the a subset of the galFiltered network organized by node degree.

Group Attributes Layout

• 

The Group Attributes layout is similar to the Attribute Circle layout described above except that instead of a single circle with all of the nodes, each set of nodes that share the same value for the column are laid out in a separate circle. The same network shown above (network generated by PSICQUIC Client) is shown above, using Layout → Group Attributes Layout → taxonomy.

Prefuse Force Directed Layout

• 

The force-directed layout is a layout based on the "force-directed" paradigm. This layout is based on the algorithm implemented as part of the prefuse toolkit provided by Jeff Heer. The algorithm is very fast and with the right parameters can provide a very visually pleasing layout. The Force Directed Layout will also accept a numeric edge column to use as a weight for the length of the spring, although this will often require more use of the Settings... dialog to achieve the best layout. This algorithm is available by selecting Layout → Prefuse Force-Directed Layout → (unweighted) or the edge column you want to use as a weight. A sample screen shot showing a portion of the galFiltered network provided in sample data is provided above.

yFiles Layouts

yFiles layouts are a set of commercial layout algorithms which are provided courtesy of yWorks. Due to license restrictions, the detailed parameters for these layouts are not available (there are no yFiles entries in the Layout → Settings...). The main layout algorithms provided by yFiles are:

yFiles Organic Layout

• 

The organic layout algorithm is a kind of spring-embedded algorithm that combines elements of the other algorithms to show the clustered structure of a graph. This algorithm is available by selecting Layout → yFiles Layouts → Organic.

yFiles Circular Layout

• 

This algorithm produces layouts that emphasize group and tree structures within a network. It partitions the network by analyzing its connectivity structure, and arranges the partitions as separate circles. The circles themselves are arranged in a radial tree layout fashion. This algorithm is available by selecting Layout → yFiles Layouts → Circular.

yFiles Hierarchical Layout

• 

The hierarchical layout algorithm is good for representing main direction or "flow" within a network. Nodes are placed in hierarchically arranged layers and the ordering of the nodes within each layer is chosen in such a way that minimizes the number of edge crossings. This algorithm is available by selecting Layout → yFiles Layouts → Hierarchical.

Layout Parameters

Many layouts have adjustable parameters that are exposed through the Layouts → Settings... menu option. The Layout Settings dialog, which allows you to choose which layout algorithm settings to adjust, is shown below. The settings presented vary by algorithm and only those algorithms that allow access to their parameters will appear in the drop-down menu at the top of the dialog. Once you've modified a parameter, clicking the Execute Layout button will apply the layout.

Edge Bend and Automatic Edge Bundling

From Cytoscape 3.0, Edge Bend is a regular edge property and can be used as a part of a Style. Just like any other edge property, you can select a Default Value, a Mapping and use Bypass for select nodes. In the Styles tab, select the Bend property from the Properties drop-down and click on either the Default Value, Mapping or Bypass cell to bring up the Edge Bend Editor. In the editor, you can add as many handles as you want to the edge using Alt-Click on Windows, Option-Click on Mac, or Ctrl-Alt-Click on Linux.

To clear all edge bends, select Layout → Clear All Edge Bends.

In addition to adding handles manually, you can use the Bundle Edges function to bundle all or selected edges automatically.

1. Select Layout → Bundle Edges → All Nodes and Edges.

2. Set parameters.

   • Details of the algorithm is described in this paper.

3. Press OK to run. Edge bundling may take a long time if the number of edges is large.

   • If it takes too long, try decreasing Maximum Iterations.

   • For large, dense networks, try setting Maximum iterations in the range of 500 - 1000.

Note: The handle locations will be optimized for current location of nodes. If you move node positions, you need to run the function again to get proper result.

Manual Layout

The simplest method to manually organize a network is to click on a node and drag it. If you select multiple nodes, all of the selected nodes will be moved together.

Rotate

• 

Selecting the Layout → Rotate option will show the Rotate window in the Tool Panel. This function will either rotate the entire network or a selected portion of the network. The image below shows a network with selected nodes rotated.

Before

• 

After

• 

Scale

• 

Selecting the Layout → Scale option will open the Scale window in the Tool Panel. This function will scale the position of the entire network or of the selected portion of the network. Note that only the position of the nodes will be scaled, not the node sizes. Node size can be adjusted using Styles. The image below shows selected nodes scaled.

Before

• 

After

• 

Align, Distribute and Stack

• 

Selecting the Layout → Align/Distribute option will open the Align and Distribute window in the Tool Panel. Align provides different options for either vertically or horizontally aligning selected nodes against a line. The differences are in what part of the node gets aligned, e.g. the center of the node, the top of the node, the left side of the node. Distribute evenly distributes selected nodes between the two most distant nodes along either the vertical or horizontal axis. The differences are again a function what part of the node is used as a reference point for the distribution. Stack vertically or horizontally stacks selected nodes with the full complement of alignment options. The table below provides a description of what each button does.

Node Movement and Placement

In addition to the ability to click on a node and drag it to a new position, Cytoscape now has the ability to move nodes using the arrow keys on the keyboard. By selecting one or more nodes using the mouse and clicking one of the arrow keys (←, →, ↑, ↓) the selected nodes will move one pixel in the chosen direction. If an arrow key is pressed while holding the Shift key down, the selected nodes will 15 pixels in the chosen direction.

What are Styles?

One of Cytoscape's strengths in network visualization is the ability to allow users to encode any table data (name, type, degree, weight, expression data, etc.) as a property (such as color, size of node, transparency, or font type) of the network. A set of these encoded or mapped table data sets is called a Style and can be created or edited in the Style panel of the Control Panel. In this interface, the appearance of your network is easily customized. For example, you can:

Specify a default color and shape for all nodes.

• 

Set node sizes based on the degree of connectivity of the nodes. You can visually see the hub of a network...

• 

...or, set the font size of the node labels instead.

• 

Visualize gene expression data along a color gradient.

• 

Encode specific physical entities as different node shapes.

• 

Use specific line types to indicate different types of interactions.

• 

Control edge transparency (opacity) using edge weights.

• 

Control multiple edge properties using edge score.

• 

Browse extremely-dense networks by controlling the opacity of nodes.

• 

Show highly-connected region by edge bundling and opacity.

• 

Add photo/image/graphics on top of nodes.

• 

Cytoscape 3 has several sample styles. Below are a few examples of these applied to the galFiltered.sif network :

Introduction to the Style interface

The Style interface is located under the Style panel of the Control Panel.

• 

This interface allows you to create/delete/view/switch between different styles using the Current Style options. The panel displays the mapping details for a given style and is used to edit these details as well.

• At the top of the interface, there is a drop-down menu for selecting a pre-defined style. There is also an Options drop-down with options to rename, remove, create and copy a Style, and an option to create a legend for the selected Style.

• The main area of the interface is composed of three tabs, for Node, Edge and Network.

• Each tab contains a list of properties relevant to the current style. At the top of the list a Properties drop-down allows you to add additional properties to the list.

• Each property entry in the list has 3 columns:

  • The Default Value shows just that, the default value for the property. Clicking on the Default Value column for any property allows you to change the default value.

  • Mapping displays the type of mapping currently in use for the property. Clicking on the Mapping column for any property expands the property entry to show the interface for editing the mapping. Details on the mapping types provided here.

  • Bypass displays any style bypass for a selected node or edge. Note that a node/edge or subset of nodes/edges must be selected to activate the Bypass column. Clicking on the Bypass column for selected node(s)/edge(s) allows you to enter a bypass for that property for selected node(s)/edge(s).

The Default Value is used when no mapping is defined for a property, or for nodes/edges not covered by a mapping for a particular property. If a Mapping is defined for a property, this defines the style for all or a subset of nodes/edges, depending on how the mapping is defined. A Bypass on a specific set of nodes/edges will bypass and override both the default value and defined mapping.

Introduction to Style

The Cytoscape distribution includes several predefined styles to get you started. To examine a few styles, try out the following example:

Step 1. Load some sample data

• Load a sample session file: From the main menu, select File → Open..., and select the file sampleData/galFiltered.cys.

• The session file includes a network, some annotations, and sample styles. By default, the style galFiltered Style is selected. Gene expression values for each node are colored along a color gradient between blue and yellow (where blue represents a low expression ratio and yellow represents a high expression ratio, using thresholds set for the gal1RGexp experiment bundled with Cytoscape in the sampleData/galExpData.csv file). Also, node size is mapped to the degree of the node (number of edges connected to the node) and you can see the hubs of the network as larger nodes. See the sample screenshot below:

• 

Step 2. Switch between different styles

You can change the style by making a selection from the Current Style drop-down list, found at the top of the Style panel.

For example, if you select Sample1, a new style will be applied to your network, and you will see a white background and round blue nodes. If you zoom in closer, you can see that protein-DNA interactions (specified with the label "pd") are drawn with dashed edges, whereas protein-protein interactions (specified with the label "pp") are drawn with solid edges (see sample screenshot below).

• 

Finally, if you select Solid, you can see the graphics below:

• 

This style does not have mappings except node/edge labels, but you can modify the network graphics by editing the Default Value for any property.

Additional sample styles are available in the sampleStyles.xml file in the sampleData directory. You can import the sample file from File → Import → Styles....

List of Node, Edge and Network Properties

Cytoscape allows a wide variety of properties to be controlled. These are summarized in the tables below.

Available Shapes and Line Styles

How Mappings Work

For each property, you can specify a default value or define a dynamic mapping. Cytoscape currently supports three different types of mappings:

1. Passthrough Mapping

   • The values of network column data are passed directly through to properties. A passthrough mapping is typically used to specify node/edge labels. For example, a passthrough mapping can label all nodes with their common gene names.

2. Discrete Mapping

   • Discrete column data are mapped to discrete properties. For example, a discrete mapping can map different types of molecules to different node shapes, such as rectangles for gene products and ellipses for metabolites.

3. Continuous Mapping

   • Continuous data are mapped to properties. Depending on the property, there are three kinds of continuous mapping:

     1. Continuous-to-Continuous Mapping: for example, you can map a continuous numerical value to node size.

     2. Color Gradient Mapping: This is a special case of continuous-to-continuous mapping. Continuous numerical values are mapped to a color gradient.

     3. Continuous-to-Discrete Mapping: for example, all values below 0 are mapped to square nodes, and all values above 0 are mapped to circular nodes.

   • However, note that there is no way to smoothly morph between circular nodes and square nodes.

The table below shows mapping support for each property.

Legend

Node Mappings

Edge Mappings

Text Passthrough Mapping

In Cytoscape 2.8.0 and later versions, the Passthrough Mapping can recognize some text representations of values. This means, if you have a string column named Node Size Values, you can directly map those values as the Node Size by setting "Node Size Values" as controlling column with Node Size "Passthrough Mapping". The following value types are supported:

• Colors: Standard color names supported by all browsers or RGB representation in hex

• Numerical Values: Automatically mapped to the specified property.

• Images: URL String. If the URL is valid and an actual image data exists there, Cytoscape automatically downloads the image and maps it to the node.

Examples

1. Color Passthrough Mapping

   • 

2. Node Size Passthrough Mapping

   • 

3. Image Passthrough Mapping

   • 

Images, Charts and Gradients

Cytoscape allows you to set custom graphics to nodes. Using the Style interface, you can map Image/Chart properties to nodes like any other property. Cytoscape provides a set of images and you can also add your own images in the Image Manager, as well as remove or modify existing ones.

Taxonomy Icon set used in this section is created by Database Center for Life Science (DBCLS) and is distributed under Creative Commons License (CC BY 2.1.)

Managing Images

The Image Manager is available under the menu option View → Open Image Manager...:

• 

• You can add images by drag-and-drop of image files and URLs. If you want to add images from a web browser or local file system, you can drag images from them and drop those images onto the list of images on the left.

  • Note: When you drag and drop images from web browser, make sure that you are actually dragging the URL for the image. In some cases, images are linked to an HTML page or scripts, and in such cases, this drag and drop feature may not work.

• If you want to add one or more images from a folder, press the + button on the bottom of the Image Manager window and then select the images you want to add.

• 

• To remove images from the current session's image library, simply select one or more images from the list and press the Remove Selected Images button (trash icon).

• Images can be resized by defining specific Width and Height values. If the Aspect Ratio box is checked, the width-height ratio is always synchronized. You can resize the image to the original size by pressing the Original button.

Using Graphics in Styles

• 

Node graphics are used and defined like any other property, through the Style interface. There are nine Image/Chart properties.

• Cytoscape provides three kinds of graphics (selectable via tabs on the Graphics dialog):

  • Images: You can select one of the provided images or add your own (click the Open Image Manager... button to add more images to the list).

  • Charts: The following chart types are available: Bar , Box, Heat Map, Line, Pie, Ring.

  • Gradients: You can also set Linear and Radial gradients to nodes.

• To add a graphic, first add one Image/Chart property to the properties list in the Style interface (on the Node tab, select Properties → Paint → Custom Paint n → Image/Chart n). Next, click the Default Value column of the Image/Chart property to bring up the Graphics dialog. Select an image, a chart or a gradient and then click Apply.

  • By default, graphics are automatically resized to be consistent with the Node Size property.

• To remove an image, chart or gradient, click the Remove Graphics button on the Graphics dialog.

• 

Graphics Positions

Each Image/Chart property is associated with a position. You can edit its position by using the UI available in the Default Value column for the Image/Chart Position property that has the same number. For instance, the Image/Chart Position 2 value modifies the position of Image/Chart 2.

• Note: Setting graphics positions for Linear or Radial gradients has no effect, as they are always centered on the node.

Z-Ordering

The number that appears with the Image/Chart property represents an ordering of layers. Basic node color and shape are always rendered first, then node Image/Chart 1, 2, ..., through 9.

Saving and Loading Images

In general, saving and loading images is automatic. When you quit Cytoscape, all of the images in the Image Manager will be saved automatically. There are two types of saving:

1. To a session file

   • When you save the current session to a file, the images used in the current styles will be saved to that file. For example, if you have a style with a discrete mapping for Image/Chart 1, all images used in the style will be saved to the session file. Other images will not be saved in your session file. This is because your image library can be huge when you add thousands of images to the Image Manager and it takes a very long time to save and load the session file.

2. Automatic saving to CytoscapeConfiguration/images3 directory

   • When you select File → Quit (Windows and Linux) or Cytoscape → Quit Cytoscape (Mac OS X), all of the images in the Image Manager will be saved automatically to your Cytoscape settings directory. Usually, they are saved in YOUR_HOME_DIRECTORY/CytoscapeConfiguration/images3.

In any case, images will be saved automatically to your system or session and will be restored when you restart Cytoscape or load a session.

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Styles Tutorials

The following tutorials demonstrate some of the basic Style features. Each tutorial is independent of the others.

Tutorial 1: Creating a Basic Style and Setting Default Values

The goal of this tutorial is to learn how to create a new Style and set some default values.

1. Load a sample network: From the main menu, select File → Import → Network → File..., and select sampleData/galFiltered.sif.

2. Create some node/edge statistics: The Network Analyzer calculates some basic statistics for nodes and edges. From the main menu, select Tools → Network Analyzer → Network Analysis → Analyze Network, and click OK. Once the result is displayed, simply close the window. All statistics are stored as regular table data.

3. Select the Style panel in the Control Panel.

   

4. Create a new style: Click the Options drop-down, and select Create New Style. Enter a name for your new style when prompted.

   

Since no mappings are set up yet, only default values are defined for some of the properties. From this panel, you can create node/edge mappings for all properties.

5. Change the default node color and shape: To set the default node shape to triangles, click the Default Value column for the Shape property. A list of available node shapes will be shown. Select the Triangle item and click the Apply button. You can edit other default values in the same way. In the example shown below, the node shape is set to Round Rectangle, while Fill Color is set to white. The new Style is automatically applied to the current network, as shown below.

   

Tutorial 2: Creating a New Style with a Discrete Mapping

Now you have a network with a new Style. The following section demonstrates how to create a new style that has a discrete mapping. The goal is to draw protein-DNA interactions as dashed lines, and protein-protein interactions as solid lines.

1. Find the property: In the Edge tab of the Style panel, find the Stroke Color (Unselected) property. If it is not already visible in the properties sheet, add it by selecting the drop-down item Properties → Paint → Color (Unselected) → Stroke Color (Unselected).

2. Choose a data column to map to: Expand the entry for Stroke Color (Unselected) by clicking the arrow icon on the right. Click the Column entry and select "interaction" from the drop-down list that appears.

3. Set the mapping type: Under Mapping Type, select "Discrete Mapping". All available column values for "interaction" will be displayed, as shown below.

   

4. Set the mapped values: Click the empty cell next to "pd" (protein-DNA interactions). On the right side of the cell, click on the ... button that appears. A popup window will appear; select green or similar, and the change will immediately appear on the network window.

   

Repeat step 4 for "pp" (protein-protein interactions), but select a darker color. Then repeat steps 3 through 4 for the Line Type property, by selecting the correct line style ("Dash" or "Solid") from the list.

Now your network should show "pd" interactions as dashed green lines and "pp" interactions as solid lines. A sample screenshot is provided below.

Tutorial 3: Creating a New Style with a Continuous Mapping

At this point, you have a network with some edge mappings. Next, let's create mappings for nodes. The following section demonstrates how to create a new style using a continuous mapping. The goal is to superimpose node statistics (in this example, node degree) onto a network and display it along a color gradient.

1. Find the property: In the Node tab of the Style panel, find the Fill Color property. If it is not already visible in the properties sheet, add it by selecting the drop-down item Properties → Paint → Fill Color.

2. Set the node table column: Expand the entry for Fill Color by clicking the arrow icon on the right. Click the Column entry and select "Degree" from the drop-down list that appears.

3. Set the mapping type: Set the "Continuous Mapping" option as the Mapping Type. This automatically creates a default mapping.

   

4. Define the points where colors will change: Double-click on the black-and-white gradient rectangle next to Current Mapping to open the Continuous Mapping Editor. Note the two smaller triangles at the top of the gradient.

   

5. Define the colors between points: Double-click on the larger leftmost triangle (facing left) and a color palette will appear. Set the color white and repeat for the smaller left-side triangle. For the triangle on the right, set the color green and then choose the same color for the smaller right-side triangle.

   

The color gradients will immediately appear on the network. All nodes with degree 1 will be set to white, and all values between 1 and 18 will be painted with a white/green color gradient (see the sample screenshot below).

• 

• Repeat for other properties: You can create more continuous mappings for other numeric table data. For example, edge data table column "EdgeBetweenness" is a number, so you can use it for continuous mapping. The following is an example visualization which mapps Edge Width to "EdgeBetweenness".

  

Tutorial 4: Setting Automatic Values to a Discrete Mapping

The goal of this section is to learn how to generate automatic values for discrete mappings.

1. Switch the Current Style to Minimal. Now your network looks like the following:

   

2. Create a discrete mapping for Fill Color. Select "AverageShortestPathLength" (generated by the Network Analyzer) as the controlling property.

3. Right-click the Fill Color cell, then select Mapping Value Generators → Rainbow. Cytoscape will automatically generate different colors for all the property values as shown below:

   

4. Create a discrete mapping for Label Font Size. Select "AverageShortestPathLength" as controlling property (Column field).

5. Right-click the Label Font Size cell, then select Mapping Value Generators → Number Series. Type 3 for the first value and click OK. Enter 3 for increment.

6. Apply Layout → yFiles Layouts → Organic. The final view is shown below:

   

This mapping generator utility is useful for categorical data. The following example shows a discrete mapping that maps the species column to node color.

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Tutorial 5: Using Images in Styles

This tutorial is a quick introduction to the node image feature. You can assign up to nine images per node as a part of a Style.

1. In this first example, we will use the presets that Cytoscape 3 has. In general, you can use any type of bitmap graphics. User images should be added to the Image Manager before using them in a Style.

2. If you are continuing from the previous tutorials, skip to the next step. Otherwise, load a network and run the Network Analyzer (Tools → Network Analyzer → Network Analysis → Analyze Network...). This creates several new table columns (statistics for nodes and edges).

3. Click the Style panel in the Control Panel, and select the Solid style.

4. If the property Image/Chart 1 is not in the properties sheet yet, add it from the drop-down Properties → Paint → Custom Paint 1 → Image/Chart 1.

   

5. Click the Default Value cell of the Image/Chart 1 entry in order to open the Graphics dialog.

   

6. Select any of the images from the list and click Apply.

   

7. Click the Default Value cell of node Transparency and set the value to zero.

8. Set the Default Value of node Size to 80.

9. Set the Default Value of node Label Font Size to 10, to increase readability.

10. Also change the edge Width to 6. Now your network looks like the following:

    

11. Open the Image Manager under View → Open Image Manager.... Drag and Drop this icon to the image list which automatically adds it to the manager.

    

12. Create a Continuous Mapping for Image/Chart 2 and select "BetweennessCentrality" as its controlling property. Double-click the Current Mapping value cell to open the Continuos Mapping Editor.

    

13. In the Continuos Mapping Editor, add a handle position by clicking in the Add button, and move the handle to 0.2. Double-click the region over 0.2 and set the new icon you have just added in the last step.

    

14. Add the property Image/Chart Position 2 from the drop-down option Properties → Paint → Custom Paint 2 → Image/Chart Position 2. Click its Default Value cell to move the position of the graphics to upper left.

    

    Now the important nodes in the network (nodes with high betweenness centrality) are annotated with the icon:

    

Tutorial 6: Creating Node Charts

The goal of this tutorial is to learn how to create and customize node charts from data stored in the Node tables.

1. Start a new session and load a sample network. From the main menu, select File → Import → Network → File..., and select sampleData/galFiltered.sif.

2. Create some node/edge statistics using the Network Analyzer. Network Analyzer calculates some basic statistics for nodes and edges. From the main menu, select Tools → Network Analyzer → Network Analysis → Analyze Network..., and click OK. Once the result is displayed, simply close the window. All statistics are stored as regular table data.

3. Select the Style panel in the Control Panel.

4. Create a new style: Click the Options drop-down, and select Create New Style. Enter a name for your new style when prompted.

5. If the property Image/Chart 1 is not in the properties sheet yet, add it from the drop-down Properties → Paint → Custom Paint 1 → Image/Chart 1.

   

6. Click the Default Value cell of the Image/Chart 1 entry in order to open the Graphics dialog.

   

7. Click the Charts tab and make sure the Bar Chart option is selected.

   

8. Select data columns: Now you have to choose the columns in the Node table that contains the data you want to be displayed as charts. The Available Columns list displays all node columns that can be used as chart data (i.e. single or list columns of numerical types).

   • First click the Remove All button to remove the current selected columns (by default, Cytoscape selects the first column in the Available Columns list).

     

   • Now select all centrality and coefficient columns from Available Columns list and click the Add Selected button.

     

9. Click the Apply button to create bar charts with the selected data columns and default options.

   

10. The network view doesn't look so good yet, so let's make a few changes to its Style before we continue. In the example shown below, the node Shape is set to Rectangle, while the node Fill Color is set to white.

    

11. Focus on one node to see the chart details. For example search for and then focus on node "YMR043W".

    

12. Change other chart options: Click the Default Value cell of the Image/Chart 1 property again in order to open the Graphics dialog, and then select the Options tab on the Bar Chart editor.

    
    On this panel, you can:

    • Choose another Color Scheme or set all the colors individually (just click on each color).

    • Show/Hide Value and Domain Labels and also set the Domain Label Position.

    • Change the chart Orientation.

    • Show/Hide Axes.
    • Change the line width and color for axes and bars.
    • Increase or reduce the separation between bars (up to 50% of the total chart width).

    • Note: Other charts provide different options.

13. Check both Show Domain Axis and Show Range Axis and apply the graphics again. Now the node chart should look like this:

    

14. The default domain labels are not very useful, so let's set better labels:

    • On the Node Table (Table Panel), create a new List Column of type String and name it "domain_labels".

    • Edit any of the cells of the created column (double-click it) and type ["Bet. Cent.","Closen. Cent","Clust. Coeff.","Topol. Coeff."].

    • Right-click the same cell and select the option Apply to entire column.

    

    • Open the chart editor again and select the Options panel.

    • Select "domain_labels" on the Domain Labels Column drop-down button.

    • Select "Up 45^o" on the Domain Labels Position drop-down button. The labels should look like this now:

    

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Advanced Topics

Discrete Mappings

Several utility functions are available for Discrete Mappings. You can use these functions by right-clicking on any property entry (shown below).

Automatic Value Generators

• Mapping Value Generators - Functions in this menu category are value generators for discrete mappings. Users can set values for discrete mappings automatically by selecting these functions.

  • Rainbow and Rainbow OSC - These functions try to assign as diverse a set of colors as possible for each data value.

    • 

  • Random Numbers and Random Colors - Randomized numbers and colors.

  • Number Series - Set a series of numbers to the specified mapping. Requires a starting number and increment.

    • 

  • Fit label width - This function is only for node Width and Size. When a discrete mapping for node Width or Size is available, you can fit the size of each node to its label automatically by selecting this function. See the example below:

    • 

Edit Selected Values at Once

You can set multiple values at once. First, you need to select discrete mapping rows in which you want to change values then right-click and select Edit → Edit Selected Discrete Mapping Values. A dialog pops up and you can enter the new value for the selected rows.

Working with Continuous Mapping Editors

There are three kinds of Continuous Mapping Editors. Each of them are associated with a specific property type:

Range Settings Panel

Each continuous mapping editor has a range settings section (labelled Edit Handle Positions and Values) with the following fields and buttons.

1. Handle Position - This box displays the current value for the selected slider handle. You can also directly type the value in this box to move the slider to an exact location.

2. Set Min and Max... - Click this button to set the overall range of this editor. The first time you open the editor, the Min and Max values are set by the range of the data column you selected (i.e. the minimum and maximum values of the mapped column).

3. Add - Adds a new handle to the editor.

4. Delete - Deletes the selected handle from the slider widget.

5. Handle Value (e.g. Node Fill Color) - Click this button to edit the value (e.g. a color) assigned to the selected handle.

Gradient Editor

The Gradient Editor is an editor for creating continuous mappings for colors. To change the color of each region, just double-click the handles (small triangles on the top). A Color gradient will be created only when the editor has two or more handles (see the example below).

Continuous-Continuous Editor

The Continuous-Continuous Editor is for creating mappings between numerical data and numerical properties (e.g. size, transparency). To change the value assigned on the Y-axis (the property shown in the example above is edge Width), drag the small squares or double-click them to directly type an exact value.

Continuous-Discrete Editor

The Continuous-Discrete Editor is used to create mappings from numerical column values to discrete properties, such as fonts, shapes, or line styles. To edit a value for a specific region, double-click the icon on the track.

Managing Styles

All Cytoscape Style settings are initially loaded from a default file that cannot be altered by users. When users make changes to the properties, a session_syle.xml file is saved in the session file. This means that if you save your session, you will not lose your properties. No other style files are saved during normal operation.

Saving Styles

Styles are automatically saved with the session they were created in. Before Cytoscape exits, you will be prompted to make sure you save the session before quitting. It is also possible to save your styles in a file separate from the session file. To do this, navigate to the menu option File → Export → Styles..., and save the selected styles to a file. This feature can be used to share styles with other users.

You can also change the default list of styles for all future sessions of Cytoscape. To do this, click the Options drop-down in the Style section, and select Make Current Styles Default. This will save the current styles as a default_vizmap.xml file to your CytoscapeConfiguration directory (found in your home directory). These styles will then be loaded each time Cytoscape is started.

Style File Formats

The Cytoscape-native Style format is Style XML. If you want to share Style files with other Cytoscape users, you need to export them to this format.

From version 3.1.0 on, Cytoscape can also export Cytoscape.js compatible JSON file. Since Cytoscape.js is an independent JavaScript library, and there are some differences between Cytoscape and Cytoscape.js, not all properties are mapped to JSON. The following properties are not supported by the exporter:

• Custom Graphics and their locations
• Edge Bends
• Nested Networks
• Network Background (Note: This can be set manually as standard CSS in Cytoscape.js)

The Continuous-Discrete Editor is used to create mappings from numerical data values to discrete properties, such as fonts, shapes, or line styles. To edit a value for a specific region, double-click on the icon on the track.

Importing Styles

To import existing styles, navigate to the menu option File → Import → Styles... and select a styles.xml (Cytoscape 3 format) file. Imported properties will supplement existing properties or override existing ones if the properties have the same name. You can also specify a style file using the -V command line option. Properties loaded from the command line will override any default properties. Note that legacy .props files can only be loaded via the File → Import → Styles... menu, but not by command line.

What are apps?

Cytoscape's capabilities are not fixed. They can be expanded with apps. They can extend Cytoscape in a variety of ways. One app can have the ability to import data from an online database. Another app could provide a new method for analyzing networks. You can install apps after you have installed Cytoscape. Most apps were made by Cytoscape users like you.

If you're familiar with Cytoscape 2.x, you probably know that Cytoscape apps were called plugins. Starting in Cytoscape 3.0, we are calling them apps. Cytoscape 2.x plugins cannot be used in Cytoscape 3.0.

Installing Apps

You can install apps through the App Store or within Cytoscape. In this section, we'll talk about installing apps through Cytoscape. You can learn how to install apps through the App Store here.

To install apps within Cytoscape, go to the menu bar and choose Apps → App Manager. At the top of the App Manager window, make sure you have the Install tab selected.

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There are three ways you can find apps:

• If you know the name of an app you're looking for, enter it in the Search field. The App Manager will list the apps whose names or descriptions match the Search field in the middle panel.

• If you have a general idea of what sort of app you're looking for, double-click on the apps by tag folder, then click on one of the tags that interests you. The apps with that tag are listed in the middle panel.

• If you're not sure what sort of app you and want to see everything, click the all apps folder. In the middle pane, you will see a list of all the apps.

When you click on an app in the middle panel, the App Manager shows its short description and icon in the right panel. If you want more information about the app, click the View on App Store button on the bottom-right. If you want to go ahead and install the app, click the Install button.

If you've downloaded an app to your computer, you can install it by clicking the Install from File button on the bottom-left.

Managing your Installed Apps

You can see a list of all apps you have installed by clicking the Currently Installed tab at the top. When you click on an app in the list, you'll see a description of your app at the bottom. At the bottom, you'll see a couple buttons where you can:

• Uninstall an app. This deletes the app from your computer. If you want to reinstall the app, you will have to find it again in the Install from App Store tab or in the App Store site and reinstall it there.

• Disable an app. This temporarily disables the app. The app stays on your computer, but Cytoscape does not load it. You can enable the app by first selecting the disabled app in the list, then click Enable.

The Command Line Tool provides a simple command-line interface to Cytoscape using the Commands API. Any app that registers commands will be available through the Command Tool. The Command Tool provides two main functions: first, a Command Line Dialog is available from Tools → Command Line Dialog, that allows the user to type commands into Cytoscape and see the results in a "Reply Log".

Second, and arguably more useful, it will read script files and execute them. Each line in the script file is a command that is sent to a app. Script files may be entered on the Cytoscape command line using the "-S" flag to Cytoscape, through the File → Run Script File... menu item, or through Tools → Execute Command File.

Cytoscape commands consist of three parts: a command class, or namespace; a command within that namespace; and a series of arguments or options provided as a series of name=value pairs. For example, to import an XGMML format file from the Command Line Dialog or a command script, you would use:

network import file filePath="path-to-file"

where network is the namespace, import file is the command, and there is only one argument: filePath="path-to-file". If there were more arguments they would appear on the same line separated by spaces.

The Command Tool also uses the Command API to provide help. "help" by itself will list all of the command classes (or namespaces) and "help " followed by a namespace will list all of the commands supported by that namespace. Details of a specific command are available by typing "help " followed by the namespace and command (e.g. "help layout force-directed"). The Command Tool registers the "command" namespace and supports a single command: run, which takes a file argument. Here is the help for the command run command from the command namespace:

help command run
       command run file=<File> 

Similarly, the help for the "network import file" example from above is:

help network import file
 network import file arguments:
 dataTypeList=<String>: List of column data types ordered by column index (e.g. "string,int,long,double,boolean,intlist" or just "s,i,l,d,b,il")
 defaultInteraction=<String>: Default interaction type
 delimiters=<ListMultipleSelection [,,;, ,\t]>: Text Delimiters
 delimitersForDataList=<ListSingleSelection (\||\|/|,)>: Text Delimiters for data list type
 file=<File>: Data Table file
 firstRowAsColumnNames=true|false: First row used for column names
 indexColumnSourceInteraction=<int>: Column for source interaction
 indexColumnTargetInteraction=<int>: Column for target interaction
 indexColumnTypeInteraction=<int>: Column for interaction type
 NetworkViewRendererList=<ListSingleSelection ()>: Network View Renderer
 RootNetworkList=<ListSingleSelection (-- Create new network collection --|Network)>: Network Collection
 startLoadRow=<int>: Start Load Row
 TargetColumnList=<ListSingleSelection ()>: Node Identifier Mapping Column

Cytoscape allows for merging of both network and table data, through Tools → Merge.

Merge Networks

The Advanced Network Merge interface is available from Tools → Merge → Networks... and allows for merging of two or more networks.

Basic Operations

• With the buttons select either "union", "intersection" or "difference".

• Networks available for merge are listed under Networks to merge. Select a network from the list and click the right arrow to transfer the network to Selected networks. Click Merge to continue. The merged network will be displayed as a separate network.

Advanced Options

The Advanced Network Merge interface includes an expandable Advanced Network Merge panel, where you can specify the details of how to merge the networks. The options available here are:

• Matching columns: This specifies the network columns that should be used for merging. Typically, the "name" column or some other column containing identifier information is used here.

• How to merge columns?: A table lets the user specify for each of the individual network columns, what the corresponding column in the merged network should be named and its data type.

Merge Tables

NetworkAnalyzer computes a comprehensive set of topological parameters for undirected and directed networks, including:

• Number of nodes, edges and connected components.
• Network diameter, radius and clustering coefficient, as well as the characteristic path length.
• Charts for topological coefficients, betweenness, and closeness.
• Distributions of degrees, neighborhood connectiveness, average clustering coefficients, shortest path lengths, number of shared neighbors and stress centrality.

NetworkAnalyzer also constructs the intersection, union and difference of two networks. It supports the extraction of connected components as separate networks and the removal of self-loops.

Network Analysis

Analyze Network

To run NetworkAnalyzer, select Tools → NetworkAnalyzer → Network Analysis → Analyze Network.

The NetworkAnalyzer will determine whether your network contains directed or undirected edges. At this point, you can choose to ignore edge direction information.

When results are calculated, they will appear in the Results Panel.

The results have multiple tabs. Details on the network parameters can be found here.

• Simple Parameters

• Node Degree Distribution

• Avg. Clustering Coefficient Distribution

• Topological Coefficients

• Shortest Path Distribution

• Shared Neighbors Distribution

• Neighborhood Connectivity Distribution

• Betweenness Centrality

• Closeness Centrality

• Stress Centrality Distribution

You can also save the statistics for later use by using the Save Statistics button.

Analyze Subset of Nodes

An exhaustive topological analysis of very large networks can be a time consuming task. The computation of local parameters for the nodes is significantly faster than the computation of global (path-related) parameters. Examples of local parameters are node degree, neighborhood connectivity, topological and clustering coefficients. Betweenness and closeness centralities, as well as stress, are global parameters.

NetworkAnalyzer provides the Analyze Subset of Nodes option for computing local parameters for a subset of nodes. If one or more nodes in the network are selected before starting an analysis, only the sub-network induced by the selected nodes is analyzed. Moreover, only local parameters are computed. Shared neighbors distribution and shortest path lengths distribution, among others, are not displayed in the results.

Batch Analysis

The Batch Analysis option is used to perform topological analysis on all networks stored in specific directory, using all possible interpretations for every network. Batch analysis consists of three simple steps:

• Selecting directories: The user selects the input and output directories. The input directory should contain network files that can be loaded into Cytoscape. Sub-directories of the input directory are not considered. The output directory is the one that will contain all analysis results after the batch analysis. In order to avoid file overwriting, NetworkAnalyzer requires that the output directory is empty (contains no files) before the batch analysis starts.

• Analysis: NetworkAnalyzer scans the input directory and loads all supported networks into Cytoscape, one at a time. Each loaded network is inspected and then it is analyzed considering all possible interpretations for it. The analysis step is complete after all networks are analyzed. Note that depending on the number of networks and their sizes, this might be a very time-consuming step.

• Inspection of results: After the analysis is complete, the button Show Results is enabled, and it displays the results dialog. The dialog contains a table of all topological analyses performed. Every row in the results table lists the loaded network, its interpretation and the resulting network statistics file that was saved in the output directory. By clicking on a network name and on statistics file name, the user can load the network and topology analysis results, respectively.

Load Network Statistics

Existing network statistics can be loaded from a file saved previously in NetworkAnalyzer.

Plot Parameters

The Plot Parameters dialog offers a possibility to plot two parameters against each other. The parameters to be plotted can be chosen from two drop-down menus. The Table Column 1 menu provides the values for the domain/category axis, and the Table Column 2 menu specifies the values for the range/value axis. The plot is updated each time a different parameter is selected in one of the menus.

Generate Style from Statistics

NetworkAnalyzer computed parameters can be visualized as node/edge size and color, if the Store node / edge parameters in node / edge table option in NetworkAnalyzer Settings is enabled. Parameters loaded from a .netstats file cannot be visualized because the network itself is not stored in the network statistics file. If, after performing topological analysis, the network is modified by introducing or removing nodes or edges, it is recommended (and sometimes required) to run NetworkAnalyzer again before visualizing any parameters.

The visualization is initiated by the Generate Style from Statistics... menu option. There are two ways of mapping computed parameters.

• Map to node / edge size: The computed parameter is mapped to the size of the nodes or edges. Mapping can be straight or inverse, that is, low parameter values can be mapped to small sizes or to large sizes. The smallest node size is set to 10 and the largest one to 100. Regarding edges, size reflects the edge line width and varies between 1 and 8. Refer to the Styles section for details.

• Map to node / edge color: A computed parameter is mapped to the color of the nodes or edges. Two mapping styles are possible - mapping low parameter values to bright colors or to dark colors. By default, the brightest color is green and the darkest color is red. The mapping also uses a middle (intermediate) color, which allows for fine-grained perception of differing values through the color gradient. The default middle color is yellow.

NetworkAnalyzer Settings

The following settings can be configured by the user:

• Store node / edge parameters in node / edge table: For every node in a network, NetworkAnalyzer computes its degree (in- and out-degrees for directed networks), its clustering coefficient, the number of self-loops, and a variety of other parameters. NetworkAnalyzer also computes edge betweenness for each edge in the network. If the respective options are enabled, NetworkAnalyzer can stores the computed values as columns of the corresponding nodes and edges. This enables the users to use the values in Styles or to select nodes or edges based on the values. A complete list of the computed node and edge columns is available here.

• Use expandable dialog interface for the display of network statistics: If this option is enabled, analysis results are presented in a window in which all charts are placed below each other in expandable boxes. If this option is disabled, analysis results are presented in a window that contains tabs for the group of simple parameters and for every complex parameter (default). Users who wish to simultaneously view two or more complex parameters of one network, should enable this option.

• NetworkAnalyzer allows the user to change the default colors of parameter visualization.

  • Background color for parameter visualization: The color of the background in the network view. It is initially set to the default Cytoscape background color.

  • Bright color to map parameters: This color defines the brightest color that parameters can be mapped to. By default its value is green.

  • Middle color: This color defines the intermediate color, that parameters can be mapped to. By default its value is yellow.

  • Dark color: This color defines the darkest color that parameters can be mapped to. By default its value is red.

• Location of the help documents: URL of the original help web page for NetworkAnalyzer. This also enables the local download and storage of this help page.

Subnetwork Creation

NetworkAnalyzer allows for the creation of sub-networks of connected components. The user selects a number of connected components from a list and each selected components is visualized as a sub-network.

Managing Properties

The Cytoscape properties editor, accessed via Edit → Preferences → Properties…, is used to specify default properties. Any changes made to these properties will be saved in .props files under the CytoscapeConfiguration subdirectory of the user's home directory.

Cytoscape properties are configurable using the Add, Modify and Delete buttons as seen below.

• 

App properties may also be edited in the same way as editing Cytoscape properties. For example, to edit the properties of Linkout, select 'linkout' from the combobox of the Preferences Editor. Some apps may store properties inside session files in addition to (or instead of) storing them in the CytoscapeConfiguration directory.

• 

Managing Bookmarks

Cytoscape contains a pre-defined list of bookmarks, which point to sample network files located on the Cytoscape web server. Users may add, modify, and delete bookmarks through the Bookmark manager, accessed by going to Edit → Preferences → Bookmarks….

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There are currently several types of bookmarks (based on data categories), including network and table. Network bookmarks are URLs pointing to Cytoscape network files. These are normal networks that can be loaded into Cytoscape. Table bookmarks are URLs pointing to data table files.

Managing Proxy Servers

You can define and configure a proxy server for Cytoscape by going to Edit → Preferences → Proxy Settings….

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After the proxy server is set, all network traffic related to loading a network from URL will pass through the proxy server. Cytoscape apps use this capability as well. The proxy settings are saved in cytoscape3.props. Each time you click the OK button after making a change to the proxy settings, an attempt is made to connect to a well known site on the Internet (e.g., google.com) using your settings. For both success and failure you are notified and for failure you are given an opportunity to change your proxy settings.

If you no longer need to use a proxy to connect to the Internet, simply set the Proxy type to "direct" and click the OK button.

Managing Group View

The configuration of Cytoscape group view may also be edited through Edit → Preferences → Group Preferences….

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