W3C home > Mailing lists > Public > w3c-rdfcore-wg@w3.org > May 2002

Re: RDF Graph questions

From: patrick hayes <phayes@ai.uwf.edu>
Date: Wed, 29 May 2002 13:32:59 -0500
Message-Id: <p05111727b91acdcd6fa8@[]>
To: Brian McBride <bwm@hplb.hpl.hp.com>
Cc: w3c-rdfcore-wg@w3.org

>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
>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.

OK, I guess. Suppose P is associated with one namespace in one graph 
and a different one in another graph, what happens if we merge the 
two graphs?

>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>
>   <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.

They do? Doesn't the xmlns:  just specify a prefix to be used in 
interpreting the foo: notation in the document? Surely there isn't 
any implication that http://example.org/ba  means anything at all by 
itself, is there (??)

>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.

I agree.

>  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.

I like this.

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Received on Wednesday, 29 May 2002 14:32:52 UTC

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