Status: This page is of historical value only. The Information Visualization project at CWI stopped in the year 2001; the main participants of the project (Guy Melançon, Scott Marshall, Bèhr de Ruiter and Ivan Herman) have moved to other projects either within or outside of CWI. Unfortunately, some of the links may not work any more either, apologies for that.

Information Visualization

Summary of contents


What is Graph Visualization?

Graph Visualization is the visualization of a set of data with relations between elements. The term graph here refers to a set of  nodes connected by edges, as opposed to the use of the term to refer to a scatter plot or "bargraph". For most people, the term "Graph Drawing" elicits an image of the classic textbook style drawings of graphs. But there are many approaches to viewing such data including less obvious methods such as 3D scenes, cityscapes, nested boxes and cubes, and alternative geometries.

Graph visualization has many areas of application. Most people have encountered a file hierarchy on a computer system. A file hierarchy can be represented as a tree (a special type of graph). It is often necessary to navigate through the file hierarchy in order to find a particular file. Anyone who has done this has likely experienced a few of the problems involved in graph visualization: "Where am I?" "Where is the file that I'm looking for?" Other familiar types of graphs include the hierarchy illustrated in an organizational chart and taxonomies which portray the relations between species. Web site maps are another application of graphs as well as browsing history. In biology and chemistry, graphs are applied as evolutionary trees, phylogenetic trees, molecular maps, genetic maps, biochemical pathways and protein functions. Other areas of application include object-oriented systems (class browsers), data structures (compiler data structures in particular), real-time systems (state-transition diagrams, Petri nets), data flow diagrams, subroutine-call graphs, entity relationship diagrams (e.g. UML and database structures), semantic networks and knowledge-representation diagrams, project management (PERT diagrams), logic programming (SLD-trees), VLSI (circuit schematics), and document management systems. Note that the information isn't always guaranteed to be in a purely hierarchical format - this necessitates techniques which can deal with more general graphs (those which aren't necessarily trees).

Visualization which involves data points without relations (such as vector fields) or with an inherent geometry such as data from MRI (magnetic resonance imaging i.e. a type of medical scan), is usually referred to as Scientific Visualization and considered a separate area of research from Information Visualization.

If you would like to know more about Graph Visualization please take a look at the (old) online version of our survey paper (html format, 150K) or the web version of our slides from a presentation at Eurographics'99. You can also find the most recent version in PDF format in the section Papers. See also our collection of links for pointers to many interesting sites describing current research or existing visualization systems.

Information Visualization Project Description

The activities described here take place within the CWI project INS3.2 "Information Visualization". See the departmental CWI web page as well.

Our group's focus is on graph visualization. Some of the problem areas in graph visualization are:

Our current research focuses on the design of visual cues to help a user navigate and explore a set of data.The problem of graph layout and drawing is fundamental to the visualization of relational information structures. As the data set grows, the visualization problem is compounded by the need to reconcile the user's need for orientation cues with the danger of information overload. Put simply:

Graph Visualization Framework

The problems listed above are inherent not only to graph drawing but information visualization in general. We have designed a graph visualization framework (GVF) which is general enough to be applied to any type of graph, large or small. It is in the form of a set of java libraries which implement several basic modules for input, graph management, property management, layout, and rendering. Some modules may be used independently. For example, the graph management module may be used as the data structure part of a program which doesn't necessarily use visualization. A sample application called "Royere" has been built using this framework and can be altered and extended to fit the needs of other users. In October 1999, we released an "alpha minus" version to colleagues. The GVF is written in Java and our current viewer uses OpenGL although it is possible to substitute other viewers.

GraphXML - Graph Description Language and File Format

In connection with this project, we have developed a graph description language in XML, called GraphXML. The CWI report describing the language is available on-line. The GraphXML parser is also available separately as a set of Java classes, and can be downloaded either in zip or in compressed tar formats.

Latour - A Tree Visualization program

Our past efforts focused on techniques which aid in viewing trees and have resulted in a Tree Visualization application implemented in Java. More details about our work with trees and some images can be found here.

You can download the Latour application (system requirements: a Java runtime environment).


 

Images

Here are some images produced by a colleague who has used Latour to view his database structures (tree structures). These images demonstrate the limits of traditional layout algorithms i.e. at some point, the user needs to reduce the data set: [The image at the top of this page was produced by Latour as well.]

Click here to access the color images contained in the VisSym'99 paper which describes a method for producing skeletal images for directed acyclic graphs.


 

Publications

Viewers:

To view PostScript files in Windows you can use Aladdin's GsView. You will also need  Ghostscript.
To view PDF (Portable Document Format) files install Adobe Acrobat Reader.
 

Information Visualization Bibliography

We have exported our Information Visualization Bibliography to html from EndNote. Our EndNote library file is available on request.

Members of this project

dotIvan Herman
dotM.Scott Marshall
dotGuy Melançon

Group Picture

In cooperation with:

dotLaBRI, University of Bordeaux I, France (within the framework of French-Dutch joint research program "van Gogh")
dotUniversity of York, UK
dotUniversity of Nice, France
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