What Is VisTrails?

VisTrails is a new system that provides data and process management support for exploratory computational tasks. It combines features of both workflow and visualization systems. Similar to workflow systems, it allows the combination of loosely-coupled resources, specialized libraries, and grid and Web services. Similar to some visualization systems, it provides a mechanism for parameter exploration and comparison of different results. But unlike these other systems, VisTrails was designed to manage exploratory processes in which computational tasks evolve over time as a user iteratively formulates and tests hypotheses. A key distinguishing feature of VisTrails is its comprehensive provenance infrastructure that maintains detailed history information about the steps followed in the course of an exploratory task. VisTrails leverages this information to provide novel operations and user interfaces that streamline this process.

Important Features

One of our main uses for VisTrails has been exploratory visualization, but the system is much more general and provides many other features, such as:

• Flexible Provenance Architecture. VisTrails transparently tracks changes made to workflows, including all the steps followed in the exploration. The system can optionally track run-time information about the execution of workflows (e.g., who executed a module, on which machine, elapsed time etc.). VisTrails also provides a flexible annotation framework whereby you can specify application-specific provenance information.
• Querying and Re-using History. The provenance information is stored in a structured way. You have a choice of using a relational database (such as MySQL or IBM DB2) or XML files in the file system. The system provides flexible and intuitive query interfaces through which you can explore and reuse provenance information. You can formulate simple keyword-based and selection queries (e.g., find a visualization created by a given user) as well as structured queries (e.g., find visualizations that apply simplification before an isosurface computation for irregular grid data sets).
• Support for collaborative exploration. The system can be configured with a database backend that can be used as a shared repository. It also provides a synchronization facility that allows multiple users to collaborate asynchronously and in a disconnected fashion—you can check in and check out changes, akin to a version control system (e.g., SVN: http://subversion.tigris.org).
• Extensibility. VisTrails provides a very simple plugin functionality that can be used to dynamically add packages and libraries. Neither changes to the user interface nor re-compilation of the system are necessary. Because VisTrails is written in Python, the integration of Python-wrapped libraries is straightforward. For example, a single line in the VisTrails start-up file is needed to import all of VTK’s classes.
• Scalable Derivation of Data Products and Parameter Exploration. VisTrails supports a series of operations for the simultaneous generation of multiple data products, including an interface that allows you to specify sets of values for different parameters in a workflow. The results of a parameter exploration can be displayed side by side in the VisTrails Spreadsheet for easy comparison.
• Task Creation by Analogy. Analogies are supported as first-class operations to guide semi-automated changes to multiple workflows, without requiring you to directly manipulate or edit the workflow specifications.

Obtaining the software

Visit http://www.vistrails.org to access the VisTrails community website. Here you will find information including instructions for obtaining the software, online documentation, video tutorials, and pointers to papers and presentations.

VisTrails is available as open source; it is released under the GPL 2.0 license. The pre-compiled versions for Windows and Mac OS X come with an installer and include a number of packages, including VTK, matplotlib, and Image Magick. Additional packages, including packages written by users, are also available (e.g., ITK, Matlab, Metro). Developers can easily add new packages using the VisTrails plugin infrastructure.