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Re: Vocab serialization equivalences

From: Dave Beckett <dave.beckett@bristol.ac.uk>
Date: Tue, 07 Jan 2003 10:55:47 +0000
To: Art.Barstow@nokia.com
cc: www-rdf-comments <www-rdf-comments@w3.org>, Brian McBride <bwm@hplb.hpl.hp.com>
Message-ID: <21448.1041936947@hoth.ilrt.bris.ac.uk>

>>>Art.Barstow@nokia.com said:
> 
> Regarding the new docs, to address a FAQ I see, please 
> normatively state:
> 
> 1) The following are equivalent:
> 
>  <rdf:Property rdf:about="xxx"/>
>  
> and:
> 
>  <rdf:Description rdf:about="xxx">
>   <rdf:type rdf:resource="&ns-rdf;Property"/>
>  </rdf:Description>


Equivalence in RDF is only done in terms of triples of the RDF graph,
so the XML syntax doc describes this in terms of rdf/xml->triples and
so you need to look up the corresponding rules.  

Both of the above cases are handled normatively by the same grammar
production:

  7.2.11 production nodeElement:
  http://www.w3.org/TR/2002/WD-rdf-syntax-grammar-20021108/#nodeElement

For the former, S2 describes the single triple that is generated:
  xxx <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/1999/02/22-rdf-syntax-ns#Property> .

For the latter, S4 handles the single child element of
rdf:Description as a property element of the node element with URI
'xxx' by following productions:

  7.2.13 Production propertyEltList
  http://www.w3.org/TR/2002/WD-rdf-syntax-grammar-20021108/#propertyEltList

  7.2.14 Production propertyElt  
  http://www.w3.org/TR/2002/WD-rdf-syntax-grammar-20021108/#propertyElt

  7.2.21 emptyPropertyElt
  http://www.w3.org/TR/2002/WD-rdf-syntax-grammar-20021108/#emptyPropertyElt

and then the single triple generated is handled by the 'Otherwise'
clause of 7.2.1, setting the triple object r to the URI in the
rdf:resource attribute.


> 2) The following are equivalent:
> 
>  <rdfs:Class rdf:about="xxx"/>
> 
> and:
> 
>  <rdf:Description rdf:about="xxx">
>   <rdf:type rdf:resource="&ns-rdfs:Class"/>
>  </rdf:Description>
> 
> The Syntax doc kind'a skirts around this informatively [1] but 
> it seems to be limited to RDF (and not include RDFS/RDFV).  

The same productions apply here.

> Perhaps a generic, normative rule like the following would 
> also be useful:
> 
>    <NS:XXX rdf:about="#NNN"/>
> 
> expands/equates to
> 
>    <rdf:Description rdf:about="#NNN">
>       <rdf:type rdf:resource="&NS;XXX"/>
>    </rdf:Description>
> 
> where of course '&NS;' expands to the full namespace URI
> bound to the prefix 'NS:'.
> 
> Regards,
> 
> Art Barstow
> ---
> 
> [1] http://www.w3.org/TR/2002/WD-rdf-syntax-grammar-20021108/#section-Syntax-typed-nodes


Section 2 is full of examples but doesn't actually show one with an
entirely empty node element (without child property elements or
property attributes) since it can only make a single rdf:type triple.
The running example didn't have such an arc and that is mostly why
that form isn't given.


I could add something in
  http://www.w3.org/TR/2002/WD-rdf-syntax-grammar-20021108/#section-Syntax-typed-nodes
showing Example 15 rewritten as two triples like:

<?xml version="1.0" encoding="utf-8"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:dc="http://purl.org/dc/elements/1.1/"
         xmlns:ex="http://example.org/stuff/1.0/" >
  <rdf:Description rdf:about="http://example.org/thing">
    <dc:title>A marvelous thing</dc:title>
  </rdf:Description>

  <rdf:Description rdf:about="http://example.org/thing">
    <rdf:type rdf:resource="http://example.org/stuff/1.0/Document"/>
  </rdf:Description>
</rdf:RDF>

and then in the further compacted form:

<?xml version="1.0" encoding="utf-8"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:dc="http://purl.org/dc/elements/1.1/"
         xmlns:ex="http://example.org/stuff/1.0/" >
  <rdf:Description rdf:about="http://example.org/thing">
    <dc:title>A marvelous thing</dc:title>
  </rdf:Description>

  <ex:Document rdf:about="http://example.org/thing" />
</rdf:RDF>

if you think that would help explain it?

Would it be better to have this as a new section such as
"Empty Typed Node Elements"?

Dave
Received on Tuesday, 7 January 2003 05:57:58 GMT

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