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Re: Metadata, XML, and RDF

From: Stefan Decker <stefan@DB.Stanford.EDU>
Date: Mon, 15 Nov 1999 17:07:41 -0800
Message-Id: <>
To: www-rdf-interest@w3.org

>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 
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 

>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 
However, RDF is more a frame-system, talking about classes, instances, 
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.

Received on Monday, 15 November 1999 20:07:49 UTC

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