The Semantics of Semantics

Bill Jarrold of SRI sent me some comments about my presentation on the 13th (see below), and I'd like to respond. He said the presentation was pretty good, but noted:

Some people will differ with your characterization that OWL contains no semantics. People are working on adding rules to OWL and OWL-Full is quite descriptive. OWL-DL is much weaker, but is computationally pretty good (description logics run in polynomial time). But, in spirit, you are right. From what little I know, Tim Berners Lee seems to urge everyone to keep moving, that through common use we will eventually arise at some sort of folksonomy like effect.

Okay, I want to clarify what I meant when I was talking about Semantic Web standards.

With regard to representing the meaning in documents, I made the claim that, despite a number of new W3C standards, we're in the same situation as we were with Electronic Data Interchange (EDI) 20 years ago. That's not true. The W3C standards are actually a huge advance over EDI (by which I really mean X12). Currently, however, they don't aim to deal with the issue of a common vocabulary that (within the business domain) EDI focused on for 25 years. There is nothing inherent in the W3C standards that keeps us from taking that extra step, so I'm excited that the Cyc Foundation will be able to offer a part of the solution to that issue.

People often talk about the Semantic Web by comparing "syntax" to "semantics." I divide the knowledge representation problem into syntax, vocabulary, ontology and semantics (as defined in my previous blog post). It's not completely accurate, but accuracy can be the enemy of clarity sometimes. :-)

OWL has support for semantics. OWL-Full has a quite a bit more support for semantics than OWL-DL. Neither contains a lot of meaning about things in the world, because the intention is to rely on ontologies expressed in OWL. It is up to users of OWL to add the meaningful terms that depend on the semantics that OWL provides.

As a result, we have a proliferation of ontologies from which, it is hoped, a common set of meaningful terms will emerge. At this point, there is some meaning in each of the ontologies, but there is not a shared meaning across ontologies.

I'm going to save discussion of folksonomies and emergent semantics for another post. For now, suffice it to say: I don't oppose ground-up development of ontologies, and there is no inherent contradiction between doing that and having a unifying hub ontology. I look forward to working with the OWL community in creating a sustainable, semantically rich Web.