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   RE: [xml-dev] The triples datamodel -- was Re: [xml-dev] Semantic Webper

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  • To: Mark Baker <distobj@acm.org>, XML Developers List <xml-dev@lists.xml.org>
  • Subject: RE: [xml-dev] The triples datamodel -- was Re: [xml-dev] Semantic Webpermathread, iteration n+1
  • From: "Kirkham, Pete (UK)" <pete.kirkham@baesystems.com>
  • Date: Fri, 04 Jun 2004 10:53:11 +0100
  • Thread-index: AcRJ0ZTtFCP4VslmSImSiQ6m7dy8ygARAh7g
  • Thread-topic: [xml-dev] The triples datamodel -- was Re: [xml-dev] Semantic Webpermathread, iteration n+1

> Mark Baker
> FWIW, I've got a simple example that I like to use to describe the
> benefits of RDF/XML over XML;
> http://www.markbaker.ca/2002/09/Blog/2003/10/09/#2003-10-rdf-and-xml

According that example, RDF allows you to deduce:
># that there exists a resource of type "http://example.org/foofoo/Person"; someplace, with properties "http://example.org/foofoo/name"; and "http://example.org/foofoo/age"; with those values
># that additional properties can be added without impacting the meaning of the former interpretation,
># various other possible syntactic additions or modifications which can be used to extend the current semantics in a backwards compatible way, if desired.

I'd agree that these are highly desirable properties, which is why pretty well all of my XML applications in the last five years have used XMI, despite it's verbosity. Assuming you apply XMI encoding rules live dynamically from your metamodel rather than using XMI to generate a schema by which you validate, XMI supports both adding properties, implies a type from the container element name, allows syntactic variations, is tolerant of re-ordering and different graph serialisation mechanics.

In fact, in XMI version 2 the 'container.' part on property element names is dropped  and much of the verbosity is reduced, so the example XML fragment is also valid XMI, with almost the same semantics:
# that there exists an OBJECT of type "http://example.org/foofoo/Person"; someplace, with properties "name" and "age" with those values.
(other semantics unchanged)

Can RDF/XML be used for 'evolution' rather than addition of properties, so that something that was a real in an early version of a model is replaced in later version to (an encoded representation of the properties of) a function that returns a real? Is allowing first class properties a killer feature? Are the UML team shooting themselves in the foot by specifying XMI 2 as a production of a WXS schema from the metamodel rather than as a metamodel driven encoding mechanism?


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