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   RDF? TM? (was Re: Didier's lab report)

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  • From: Uche Ogbuji <uche.ogbuji@fourthought.com>
  • To: Nikita Ogievetsky <nogievet@cogx.com>
  • Date: Thu, 14 Dec 2000 08:52:04 -0700 (MST)

> Lets take this as an example:
> > > In the scope of WML aware client use this stylesheet,
> > > in the scope IE5 use another stylesheet
> > > and in the scope of NC and IE4  and IE3 use yet  third stylesheet.
> > > I used this approach a couple of months ago and quite successfully!.
> > > Same thing applies to the values of XSLT parameters.
> Here is XTM syntax for it (my $.02):
> <topic id="abc">
> <subjectIdentity><resourceRef xlink:href="abc.xml"/></subjectIdentity>
> <occurrence>
>  <instanceOf><topicRef xlink:href="#xslt-stylesheet"/></instanceOf>
>  <scope><topicRef xlink:href="#wml"/></scope>
>  <resourceRef xlink:href="wml.xsl"/>
> </occurrence>
> <occurrence>
>  <instanceOf><topicRef xlink:href="#xslt-stylesheet"/></instanceOf>
>  <scope><topicRef xlink:href="#ie5"/></scope>
>  <resourceRef xlink:href="ie5.xsl"/>
> </occurrence>
> <occurrence>
>  <instanceOf><topicRef xlink:href="#xslt-stylesheet"/></instanceOf>
>  <scope><topicRef xlink:href="#nc"/></scope>
>  <resourceRef xlink:href="nc.xsl"/>
> </occurrence>
> </topic>
> The "xslt-stylesheet" topic defined elsewhere specifies that this occurrence
> is XSLT stylesheet
> The "wml" scoping topic (theme) defined elsewhere specifies that "wml.xsl"
> stylesheet should be used in the scope of WML aware browsers;
> same goes for "ie5" and  "nc"
> Note that this is a very RDF-like case because the subject of the topic is a
> resource.

Sure.  And here's just one of ten vigintillion ways to express this in RDF
right in the original XML

<MyOriginElement rdf:ID="origin1">
      <incstyle:sheet incstyle:case="WML" xlink:href="wml.xslt"/>
      <incstyle:sheet incstyle:case="IE5" xlink:href="ie.xslt"
      <incstyle:sheet incstyle:case="IE4" xlink:href="ie.xslt"
      <incstyle:sheet incstyle:case="other" xlink:href="default.xslt"/>

Again, I even included a few bonuses, and it's still quite simple.  Of
course it does illustrate another of RDF's annoyances: that you must
have a namespace on all attributes if you wish to them to be considered
abbreviated properties.

And RDF is flexible enough that you can also express this without a single
"rdf" element or attribute besides the envelopes.

> (XTM topic can also have a real-world subject, one that can not be addressed
> directly.

So can RDF with anonymous resources.

> In this case "the subject may be indicated through one or more resources
> that describe the subject" -- xtm spec.)
> In any case, could you give an equivalent to the above example that uses RDF
> triples? Would you like to go for this exercise?

Your statement makes me wonder how you understand the role of "triples" in
RDF.  I get  the impression that you might not realize that they are
simply a database and list-processing convenient representation of the
RDF abstract model, which is a graph, just like TM's.

You can work with RDF just fine without worrying about constructing
"triples" if you like.  You can use the graph or the XML serialization.

Uche Ogbuji                               Principal Consultant
uche.ogbuji@fourthought.com               +1 303 583 9900 x 101
Fourthought, Inc.                         http://Fourthought.com
4735 East Walnut St, Ste. C, Boulder, CO 80301-2537, USA
Software-engineering, knowledge-management, XML, CORBA, Linux, Python


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