July 27, 2010
Recently we've been building large enterprise ontologies for our clients using the W3C web ontology language OWL. If you're not familiar with OWL, think of it as a data modeling language on steroids. It also has the fascinating property of being machine interpretable.
You can read the model with the aid of an inference engine, which not only tells you if all the assertions you have made are consistent, but also can infer additional parts of the model which logically follow from those assertions. So far the available tools for developing OWL ontologies, like Top Braid Composer and Protégé, look and feel like programming development environments. Some visualization tools are available but there is no graphical authoring tool, like Erwin or ER Studio, that data modelers have become used to.
The larger your ontology gets, the harder it is to understand and navigate using the current tools, and enterprise models push the boundaries of size and complexity for OWL ontologies. Another problem is that, because of OWL's expressiveness, the UML diagramming conventions can result in a very complex-looking diagram even for simple ontologies.
This makes it hard to review models with subject matter experts (SMEs), who typically have about 15 minutes' worth of tolerance for training in complex modeling notations. Faced with these problems, we developed our own Visio-based ontology authoring tool. It uses a more compact, more intuitive diagramming convention that is easier for SMEs to grasp.
From the diagram you can generate compliant OWL in XML format that can be read by any of the standard editors or processed by an OWL inference engine. The tool, which we call e6tOWL, is built as an add-in to Visio 2007 which provides the diagramming platform. In addition to the Visio template containing the diagramming shapes and the OWL generation function, the tool provides a lot of layout and management functionality to help deal with the challenges of maintaining large and complex diagrams.
So far the results have been good. We find it faster, easier and more fun to create ontologies graphically, and SMEs seem able to understand the diagramming conventions and provide meaningful feedback on the models. We are still using Composer and Protégé for running inference and debugging, but all our authoring is now done in Visio. We currently maintain the tool for our own use and provide it to our clients for free to help with the ongoing development and maintenance of ontologies.