Re: RDF for metadata

On Mon, 15 Oct 2001, Drew McDermott wrote:

>
> One suggested role for RDF is as metadata for XML.  (The "semantics"
> of XML as some have imprecisely said.)  The idea is that RDF (or
> RDF+rules, or RDF+DAML+OIL) would be used to make assertions that
> constrain the meaning of XML tags.  E.g., if there is a 'family' tag
> in some XML vocabulary, so we could write
>
>    <family>
>       <father><person> ...</person></father>
>       <mother><person> ...</person></mother>
>       <children>
>           <person> ...</person>
>           <person> ...</person>
>       </children>
>    </family>
>
> then we could give constraints on these symbols.  (No child has more
> than one mother, or the like.)
>
> Has anyone actully done this for any existing XML vocabulary?  Are
> there pointers to such efforts?  I'm having trouble visualizing
> exactly how RDF would do this job.

Ages ago, there was a spec submitted called DCD (Document Content
Description for XML) which basically did XML DTDs in RDF. It's not quite
what you're asking for, and was written to a now obsolete draft of the RDF
syntax spec.
http://www.w3.org/TR/NOTE-dcd


A different approach, more rules based but expressed in custom XML format,
is Schematron.
	http://www.ascc.net/xml/resource/schematron/schematron.html

Here's an example Schematron schema for 'Purchase Order':
	http://www.ascc.net/xml/resource/schematron/po-example.html
	http://www.ascc.net/xml/resource/schematron/po/po-schema.html


The rules are couched in terms of XPath-based expresssions.

For an RDF vocabulary that could the basis for a DAML+OIL model for this
sort of thing might be: http://www.w3.org/TR/xml-infoset-rdfs
(the XML Infoset represented in RDFS).

The schema itself: http://www.w3.org/2001/04/infoset

...includes declarations such as:

 <rdfs:Class ID="Element">
	  <rdfs:subClassOf resource="#InfoItem" />
  </rdfs:Class>
 <rdfs:Class ID="Attribute">
	  <rdfs:subClassOf resource="#InfoItem" />
  </rdfs:Class>
 <rdfs:Class ID="ProcessingInstruction">
	  <rdfs:subClassOf resource="#InfoItem" />
  </rdfs:Class>

There's a paper by Rick Jelliffe on using his Schematron system in a
manner similar to the app you suggest. See:

http://www.ascc.net/xml/schematron/text/prolog.html
"Logical Inference from Schematron Schemas"


Sorry for the random jumble of refs; I hope to tidy them up someday...
I'd like to write another chapter of my attempt at 'a story about RDF and
MXL' (http://www.w3.org/2001/06/rdf-xproc/1 with Eric Miller)
incorporating all this and some other interesting RDF-meets-XML apps I've
seen.

Dan


>                                              -- Drew McDermott
>

Received on Monday, 15 October 2001 12:03:22 UTC