I’m at Berliner XML Tage, an annual German-language XML and Semantic Web conference in Berlin.
The keynote by Heiner Stuckenschmidt of Universität Mannheim features a provocative title. After a recap of the 2001 SciAm paper and a short journey up and down the Semantic Web technology stack, it gets more interesting later on.
Typical Semantic Web applications of today work something like this: Information is extracted from existing data, like web pages. An ontology is built with Protégé. Some inference is done over everything, and some views generated (“Semantic Portals”). Heiner estimates that this describes 80% of current Semantic Web projects.
But that’s not “living in the Real Web”, Heiner says. We want distributed information, a P2P-like architecture, and have to deal with the possibility of failure, inconsistency, incompleteness and heterogenity of data.
Don’t do big monolithical ontologies. Ontologies should be modular.
Don’t do big monolithical servers. Things should happen distributed, e.g. based on ontology structure, that is, put related information on the same server but not everything on a single one, or leave the data and ontologies “out there” in the Web.
Don’t do big monolithical reasoning. Gathering all the data in one place to do inference is not optimal. Inference engines should sit on every node in the distributed system. (He points to C-OWL, Distributed Description Logics and the DRAGO system as possible approaches to distributed inference.)
Distributed Ontologies: Heiner thinks that OWL works well for the old scenario where ontologies are built by individual persons or organizations, but is not very good for working with distributed ontologies. There are many situations where “A is almost subClassOf B”, but in OWL, a single outliner prevents us from relating the two classes. A possible way out would be probabilistic logic.
So, what’s wrong with the Semantic Web? Too little attention has been paid to the specific needs of a distributed environment. The Semantic Web is a part of the World Wide Web.
Q: You talked about distributed ontologies. What about distributed RDF knowledge bases?
A: They exist, the need for distribution has been realized earlier in this area. There are many systems that do centralized reasoning over distributed data.
Q: Shouldn’t we concentrate more on RDF data and schema than OWL?
A: Maybe – but I’m a logician, not a database guy.
Q: (Klaus Schild) Scalability? OWL is NP-complete.
A: Distribution helps. Certain combinations of operators are deadly, but if the two operators happen to end up on different nodes, things can be much faster. But in general it’s a problem.
Q: But if you take the Web seriously, you need sub-linear complexity.
A: You can’t have that with RDF and OWL.
Isn’t it kind of odd to have a whole conference just on XML? I mean, there are a gazillion uses of XML. To me, this seems similar to having a literature conference just on the letter “e”.
Just wondering… ;-)
If we added a new letter to the alphabet, then we could very well have a conference where writers and linguists report on what they do with the letter :-) XML is no longer brand new, but still an interesting area of specialization.
But you could easily get the impression here that it’s a conference on the letter “x”.
This conference – that I am actually attending right now – seems really a little worn out. I think it will last unto next year and may then be replaced by something further on the peak of the hype cycle.