Not so alternate a view of OWL 1.1
by Bijan Parsia
I’m back in lovely Manchester, but I’ve not recovered. Full postings and discussion of ISWC, OWLED, next steps for OWL, etc. shall have to wait.
However Jim Hendler has a blog post entitled “An alternative view for Owl 1.1?” The title is phrased as a question, so I think I’ll answer it: No, the view sketched in that post is really an alternate view. Or, at least, not a disjoint view.
To present the nub, here’s a quote:
In short, either as part of OWL 1.1 or opposed to it (depending on the poilitics) we should have some people working on a clean subset of OWL that is easy to learn, easy to support, and provides useful new functionality at the data schema/controlled vocabulary level — I think this would increase OWL use and uptake, and would provide a natural path from RDF to OWL through this middle layer – providing more room (and thus more money to be made) in the OWL space.
This is good advice….so good that it’s been part of the constallation of OWL 1.1 specs for quite some time, to wit: OWL 1.1 Web Ontology Language: Tractable Fragments. These include three specifically database oriented fragments, DLP, hornSHIQ and DL-Lite. (Note that there were papers at OWL on the hornSHIQ and DL Lite families.)
Some of these already explicitly address functionality Jim is after (e.g., see inverse functional properties in DL Lite). While DLP and hornSHIQ are closely associated with Datalog (i.e., being “Datalog” fragments of OWL), DL Lite makes novel use of databases (e.g., query answering by query expansion).
Are there more fragments? Of course! Considere Herman ter Horst’s paper, Completeness, decidability and complexity of entailment for RDF Schema and a semantic extension involving the OWL vocabulary.
An aside: “tractable” is really the wrong name for this set of fragments (and not only because from some perspectivies, they aren’t). “Interesting” is better (and I think there’s wide agreement that OWL Lite failed to be usefully interesting). Some things that make, to my eyes, a fragment interesting is that it has a different “natural” implementation technique, that it has low data complexity, and that it seems to have “natural” or “useful” expressivity. All the fragments in the Tractable Fragments document arguably have (and have been argued to have) these properties.
So, clearly, the idea that it would be helpful and valuable to the OWL community to “do OWL Lite right” or rather “do the species of OWL better” is a part of the current OWL 1.1 effort. Tweaks are, of course, welcome (so I’ll be interested to see what Jim and Ora come up with). And in the very very straw charter I jotted up, additional tractable fragments or refining the current set in other ways is clearly a big part of the work of the group.
So, seems like there is agreement, not disagreement.
P.S. I am extra confused by Jim’s “p.s.” where in he writes:
And I should mention now, early, and in public, that if the “charter” being circulated for OWL 1.1 were to come to a W3C I would oppose it on the grounds that moving away from the RDF syntax is a non-starter with me – but that’s a topic for some later blog…
Given that the current set of OWL 1.1 documents include a mapping to RDF graphs which is very much inline with the current mapping of OWL to RDF graphs. So it’s hard to see it as a “moving away”.
I’ll be interested in the future blog post explaining what’s up. Obviously, adding new, normative non-RDF syntaxes that are not discouraged as an exchange format means that RDF/XML’s status as the canonical and ubiquitous exchange format is threatened. But given the greater easy of mapping back and forth between the functional/abstract syntax and RDF graphs (i.e., there is a technical improvment in the mapping to eliminate or minimize the non-determinism of the mapping), I fail to feel the bite of this. There are many circumstances where being forced to work in or exchange RDF/XML is a real problem: e.g., parsing big documents, or making use of XML technology like W3C Schema directed editing come to mind.
P.P.S. Now I really am going to bed.
