The use of OWL
by Bijan Parsia
(By OWL, I mean OWL-DL, by which I mean a suitably large fragment of OWL for which there is comprehensive reasoning support.)
I am sometimes asked, even by myself, what the glaring successes of OWL are. What’s the killer app, or the essential app, or just the app its well suited for. I was just asked this last week by some IBMers up in Cambridge.
The answer is tricky. The question is not entirely complete. One thing we certainly don’t want in the answer is anything derived entirely from (posited, future) network effects. We want some intrinsic value. Since OWL is pretty durn expressive, it is tempting to point at things you can or cannot (straightforwardly; note the KEY qualifier) say in OWL. But that key qualifier is crucial.
One aspect of OWL that stymies is its open world assumption. The OWA entails that you have to say a lot more explicitly in order to nail down certain conclusions. For example, in an OWL knowledge base (KB) where I know that Mary is either tall or short, I don’t necessarily know which. Similarly, I might know that she has three children, but there may be no “Mary parentOf xxxx” statements in the KB. Worse, a KB with the fact that Mary has (only) three children and that Mary is the parent of Monique, Carol, Esvandiar, and Megan will not be contradictory, since, for all we know, Monique and Megan are the very same child.
So, validation of this sort is definitely not a strong point of OWL. If that’s what you want, you are just in the wrong place (though, with certain extensions we can achieve much in this line).
What is OWL (and Description Logics, or similar formalisms) good for? Well, they are fairly good at representing and reasoning with partial information. Configuration is a classic application, and anything that can be reduced to a configuration problem. SAT like problems, since OWL includes propositional logic. For representing and reasoning about other (less expressive) formalisms. For example, we were able to reduce WS-Policy to OWL (since it’s just propositional logic). The advantage here wasn’t just clarifying the semantics or generating a WS-Policy checker. There are a whole suite of services that had not occured to policy folks that were obvious on the OWL side: policy containment, equivalence, disjointness and incoherence. Just being able to state more general policies is helpful, especially when the reasoner can find which other policies specialize these more general ones. (Other examples of such reductions are UML, ER diagrams, relational schemas and queries, XPath queries, and XML (though XML required some extensions).
One reason that DLs are popular in bioinformatics is that 1) the information is often structural (configuration!) and 2) one can categorize structures based on partial information. So, if you have this sort of problem, OWL might be a big win for you.
(I mention torture again! Be upset about it!) I was just reading about executions of homosexuals in Iran. (I am of Iranian descent.) Amnesty has a map of the worldwide status of sexual minority rights. It’s sad to have to hope and look forward to no part of this map being black, and to know that it is unlikely to be so in the near term.
