Re: RDF Graph questions

I basically agree with Brian's comments.

I'll also add a further comment:  even if M&S says a property must be 
associated with a namespace, it's not clear what that actually means.  My 
understanding is that the model theory binds the relational extension of a 
property to the URI, irrespective of any namespace it may be "associated" 
with.  Also, the abstract graph has URIrefs, without any associated 
namespaces.  So the two graphs you offer, under current RDF rules, I think 
must be considered abstract-syntactically and semantically equivalent.

I am also tending to a view that a '#'-separator should be preferred, and 
possibly even inserted automatically when forming a URIref from 
URI-without-trailing-separator + fragment (Jonathan Borden's 
suggestion?).  See some recent comments of mine on www-talk [1], which also 
link some off-list exchanges between myself and Pat Hayes [2].

#g
--

[1] http://lists.w3.org/Archives/Public/www-talk/2002MayJun/0032.html
     http://lists.w3.org/Archives/Public/www-talk/2002MayJun/0042.html
     http://lists.w3.org/Archives/Public/www-talk/2002MayJun/0041.html

[2] http://lists.w3.org/Archives/Public/www-archive/2002May/0018.html
     http://lists.w3.org/Archives/Public/www-archive/2002May/0019.html
     http://lists.w3.org/Archives/Public/www-archive/2002May/0020.html
and also:
     http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Feb/0494.html


At 04:46 PM 5/29/02 +0100, Brian McBride wrote:

>Sans Chapeau
>
>At 10:39 24/05/2002 +0100, you wrote:
>[...]
>
>>2. Can any URI ref be a property name or must there be some associated
>>namespace?
>
>I'm concerned that this question is not quite capturing the issue.
>As DaveB has pointed out, any URI ref can be associated with a namespace
>using rdfs:isDefinedBy.
>
>I think there is consensus that there is no syntactic restriction on the
>form of URI that can denote a property in the graph (though some graphs
>may not be serializable in RDF/XML without some schema based trickery).
>
>M&S does, in my view, clearly say that a property must be "associated" with
>a namespace.  In answer to Pat's question, my interpretation of that, is that
>M&S states it should be possible to determine what namespace is associated
>with a property.
>
>We may choose to clarify those statements in M&S.
>
>I propose the following test case.
>
>Are the following two graphs, equal?
>
>   <rdf:RDF xmlns:foo="http://example.org/b">
>     <rdf:Description>
>       <foo:ar>foobar</foo:ar>
>     <rdf:Description>
>   </rdf:RDF>
>
>and
>
>   <rdf:RDF xmlns:foo="http://example.org/ba">
>     <rdf:Description>
>       <foo:r>foobar</foo:r>
>     <rdf:Description>
>   </rdf:RDF>
>
>Our present specs would say that they are.
>
>My reading of M&S is that it says that these two fragments of RDF/XML do 
>not represent the same information as they 'associate' the uri 
>http://example.org/bar with different namespaces.
>
>Thus a "clarification" is clearly in order.
>
>It seems that there a number of possible positions, including:
>
>   1) at least one of the above fragments of xml must be wrong, as the
>      same uri can't be 'associated' with two different namespaces
>
>   2) the above fragments of xml are "equal".  (A different mechanism must be
>      used to determine the namespace associated with a URI.)
>
>Option 1 is closer to (my reading of) M&S.  I think option 2 commands more
>support in the WG and is I think, better.
>
>Propose:
>
>  o The two graphs described in the above test case are equal
>
>  o Resources which are RDF schema properties and classes MAY be described
>    in one or more associated schemas.
>
>    Designers of RDF schemas SHOULD identify their schemas with a URI
>    reference which ends in a character which cannot be part of an XML
>    localname, such as "#" or "/".
>
>    Designers of RDF schemas SHOULD identify the resources defined by
>    a schema with a URI consisting of the concatentation of the URI REF
>    of the schema with an XML localname.
>
>    The resource identified by applying algorithm A (described below) to
>    URI U MAY contain RDF schema information about the resource identified
>    by U.
>
>    The value of an isDefinedBy property of a resource MAY contain RDF
>    schema information about that resource.
>
>Algorithm A is the usual namespace splitting algorithm.
>
>The above need wordsmithing/refining, if the approach find favour with the WG.
>
>Brian

-------------------
Graham Klyne
<GK@NineByNine.org>

Received on Wednesday, 29 May 2002 16:05:26 UTC