- From: Sankar Virdhagriswaran <sv@crystaliz.com>
- Date: Mon, 15 Nov 1999 19:01:00 -0500
- To: Michael Uschold <michael.f.uschold@boeing.com>, www-rdf-interest@w3.org
As far as I know there is no white paper. There is a W3C report that compares RDF to UML. 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. 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). 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. 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. 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. So, the map as I see it as follows: At the logical schema level we went from Relational tables in the 70s, to ORDBMS structures in the 90s. This stream merged with structured document representation (a la SGML) to produce XML-Schema, XLink, XPath, etc. At the conceptual schema level we went from entity-relationship representations in the 80s to predicate calculus and object based (e.g., UML) models in the 90s (actually predicate calculus has been around since the 80s, but had not been applied in semantic mediation). Notice that conceptual models were useful only in the context of working with logical schemas. However, that was the closed world of DBMSs. On the Web, one can have completely different 'services' develop even with separation between these. Unfortunately, one is affected by mind space and resources to address both. But, hey, the world is big. Maybe the best that can come out is some set of people will work on services that leverage the logical schema level while others will offer services based on conceptual schema level. Who knows? Sankar PS: I wish the W3C would say some thing like the above or some thing that is a theory like the above to help people. This lack of theory is what folks are complaining about.
Received on Monday, 15 November 1999 19:03:03 UTC