- From: Sankar Virdhagriswaran <sv@crystaliz.com>
- Date: Mon, 15 Nov 1999 20:35:12 -0500
- To: Stefan Decker <stefan@db.stanford.edu>, www-rdf-interest@w3.org
I agree with most of what you are saying. You are also correct in saying that it is more a frame system than predicate calculus based system. But, I thought it did a decent job of unifying both of these perspectives. This is also not new. All the commercial expert system tools of circa 1984 did this (ART, KEE, etc.). Finally, when I mentioned practical applications, I was talking historically and 'commercial' applications. I am not aware of any commercial efforts that use RDF for reasoning purposes in a major way (I am aware of open directory). thanks for the clarifications. Sankar ---------- >From: Stefan Decker <stefan@DB.Stanford.EDU> >To: www-rdf-interest@w3.org >Subject: Re: Metadata, XML, and RDF >Date: Mon, Nov 15, 1999, 8:07 PM > >Hi, > >> >> >>I am sure others would have different views on this, but the way I have >>thought about this is to think of RDF as a conceptual modeling language and >>XML-Schema as a logical schema language. RDF comes from the knowledge >>representation community and hence worries a lot about semantic >>representation and reasoning through them. > >I wish that would be true. Actually, if you want to map RDF to communities, >it was initially developed as a metadata standard to represent Dublin Core >Metadata >and to supercede the PICS standard. > >However, as soon as one starts to represent information in a general, >declarative and reusable way, Knowledge Representation techniques are >indeed applicable. >And the RDF-developers did a good job, many Knowledge Representation >Formalisms are mappable to RDF, and RDF has the chance to be the >first widely used Knowledge Representation Language. >AI-folks are only partially recognizing this... > >>The most practical application of >>this sort of stuff has been in conceptual modeling languages such as UML >>(which is why reading the comparison report is interesting) and in expert >>systems (or limited versions of these). >I disagree. UML is a Software Engineering Methodology - which involves >also modelling. However, the most practical application right now is to >represent metadata >about web resources and to built search engines for this. >Indeed RDF is now used in several DigLib-projects to represent vocabularies >used for classification of documents. > >And here RDF has to prove its usefulness. > >>XML-Schema is verbose and voluminous, but is driven by the need to support >>exchange of document + ORDBMS data and with the need to support different >>namespaces for schema. There are a lot of practical applications for this >>sort of stuff. >Sure. However, it is document-centered. It defines what is allowed for a >document. > >>RDF on the other hand worries about a new way modeling resources from which >>'automated' agents could reason. One way to think about RDF is Prolog >>clauses. The analog of the Prolog unification (i.e., inferencing) is what >>automated agents that process RDF will have to write. The choice of syntax >>in RDF makes it difficult for folks who are used to the style of mark-up in >>XML and HTML. >Not prolog clauses, but maybe facts. That is indeed the way RDF is used in >SiLRI. >However, RDF is more a frame-system, talking about classes, instances, >attributes >and so on. BTW: Unification maybe regarding as Inferencing, but in this case >it is really trivial.... >RDF can be imbedded in several logical formalism, one is Horn clauses, >as e.g. implemented in one particular (not necessarily the best for RDF) >way in Prolog. > >However, this is not the first aim for RDF, but using it for reasoning is >for sure >something that can be done with it. > >>As such, representing your information in RDF allows for a lot of power and >>flexibility. As can be seen from recent traffic on this group, one can start >>with querying and go all the way up to inferencing. Furthermore, RDF Schema >>makes expression of object oriented models fairly straight forward. > >CU, > Stefan > > >
Received on Monday, 15 November 1999 20:35:03 UTC