When designing or evaluating a website, usability engineers (UE) may wish to conduct tests in which subjects are asked to perform some tasks. The UE then needs to capture and analyze the results of such tests. As discussed elsewhere, the WebVIP tool may be used to capture various aspects of subjects' behavior. VisVIP allows the UE to visualize the paths taken through the website by the subjects. This overview helps the UE to answer such questions as:

• Which parts of the website were used for the performance of a given task?
• Which parts were not used?
• How long did various subjects take to perform a task?
• How long did they take when visiting individual pages?
• How did subjects' paths compare with that of an expert?
• What is the overall linkage structure of the website?
• What patterns of navigational behavior did the subjects exhibit (e.g. re-visiting a home page, circling, etc.)?

VisVIP presents a 3D visualization of subjects' navigational path data through the website. It automatically lays out a 2D graph of the website. Each node of the graph represents a web page, and edges represent links between pages. Nodes are color-coded by type: blue for HTML, purple for directories, green for images, and so on. Because URLs tend to be long, a briefer nickname is generated for each page. The UE has several options to simplify the graph: nodes of a given type, or those not on or near a userpath, can be suppressed. Also, if a graph is highly interconnected, the UE can specify that the site be pictured as a tree emanating from a selected root node.

Once a satisfactory graph of the website has been obtained, the UE can select which userpaths to display. These paths are represented as spline curves, resting on the plane of the website graph. The time spent at each page is depicted as a dotted vertical line with its base at the appropriate node. Curvy vertical arrows into and out of the plane mark the beginning and end of each user path. Each user is assigned a unique color, so that several paths can be shown at once.

Paths resulting from simple layout over the website are often much more complex geometrically than their inherent structure would dictate. Therefore VisVIP can also arrange the graph by treating pages as adjacent iff they are connected by a userpath, rather than by the existence of a static link. The resulting display usually makes the structure of the path much simpler, albeit at the cost of complicating the display of the underlying website.

Finally, VisVIP can animate a subject's progress along the path. The UE can adjust the speed of the animation, or use a slider to directly control the time for which the path is displayed (e.g. show where the subject was after 30 seconds).

Some other useful information sources for VisVIP are:

• For a discussion of the design rationale for VisVIP, please see the paper: "VisVIP: 3D Visualization of Paths through Websites" in the HTML or Postscript version.
• For snapshots of VisVIP visualization, and other general information, please see the VisVIP Home Page.
• The Web Metrics dataflow diagram shows how VisVIP depends on other components of Web Metrics. If you are planning to install and use VisVIP, we strongly recommend that you consult this diagram, since it provides an overview of relationships among the various software components. The basic idea is that we use linklint and convert-ll.perl to find the static structure of the website of interest and WebVIP to record subjects' meanderings through that website. The information from these processes is then passed to VisVIP.

VisVIP is a tool in the Web Metrics Testbed developed at NIST. For more information, see http://www.nist.gov/webmetrics. Direct all comments and questions to webmetrics@nist.gov. Before using this tool, please review the VisVIP release notes and known bugs.

See NIST Web Metrics disclaimer.