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Re: RDF Graph questions

From: Dave Beckett <dave.beckett@bristol.ac.uk>
Date: Fri, 24 May 2002 11:04:39 +0100
To: Jeremy Carroll <jjc@hplb.hpl.hp.com>
cc: w3c-rdfcore-wg <w3c-rdfcore-wg@w3.org>
Message-ID: <3876.1022234679@tatooine.ilrt.bris.ac.uk>
>>>Jeremy Carroll said:
> Second a few questions.
> 
> 1. Are there unattached nodes in an RDF graph?

No; since we base our describe the rdf graph as triples
as node->arc->node rather than any other form.  If this is not the
case then N-Triples in insufficient to connect the model theory and
syntax.

> 2. Can any URI ref be a property name or must there be some associated
> namespace?

Any URI ref.  This is pretty clear from M&S and we've mentioned this
a few times in passing with respect to the issues related to
writing them as qnames.

(XML) Namespaces are artifacts of the RDF/XML serialization and are
not in the current model.

> 3. For XML literals should I
>    - specify that they must be well-balanced XML

Any legal XML element content
   i.e. "foo<blah/>bar" is OK as well as "<blah>foo</blah>"
since this is the kind of thing allowed inside an XML element; weaker
than just well-balanced.

>    - explicitly permit any unicode string (but only constrain equality
> for well-balanced XML)
>    - have deliberate vagueness (e.g. talk about a unicode string, and
> then only define equality on well-balanced XML and ignore the issue of
> whether other strings are permitted or not).
> 
> 
> Test cases for 1 & 2.
> 
> 1:
> 
> Is this RDF/XML document
> 
> <rdf:RDF><rdf:Description/></rdf:RDF>
> 
> equivalent to or different from this one:
> 
> <rdf:RDF/>

Yes (from the description in the syntax doc)

> and/or this one:
> 
> <rdf:RDF>
>  <rdf:Description rdf:about="http://example.org/"/>
> </rdf:RDF>

Yes (ditto)

> (the question can't be asked in N-triple)

Well, the equivalence can be made I guess?

> 2:
> 
> http://www.w3.org/2000/10/rdf-tests/rdfcore/rdfms-uri-substructure/error001.nt
> 
> whose status is pending
> 
> Is this:
> 
> a) an error because there is no such RDF graph
> 
> or
> 
> b) an example of alegal RDF graph that cannot be serialized as RDF/XML

Yes, in my opinion.  RDF/XML allows serializing of a large subset of
the legal RDF models, this is one it can't do without using some
method (such as Dan Brickely's suggestion of using subProperty)

> Reading
> http://www.w3.org/2000/03/rdf-tracking/#rdfms-uri-substructure
> 
> and our resolution is not helpful.

Dave
Received on Friday, 24 May 2002 06:07:51 EDT

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