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RE: properties as nodes etc.

From: Danny Ayers <danny666@virgilio.it>
Date: Wed, 19 Jun 2002 13:15:11 +0200
To: "Jonathan Borden" <jonathan@openhealth.org>, <www-rdf-logic@w3.org>
Message-ID: <EBEPLGMHCDOJJJPCFHEFKEMNGKAA.danny666@virgilio.it>


Thanks Jonathan.

>In RDF an edge corresponds not to the property or predicate URI but rather
>to the triple itself. Many edges may share the same predicate, so the
>predicate URI does not 'point' to or identify the edge itself.

No wonder I was getting confused re. classes and instances. The primer
doesn't help :

(2.3) "In this notation, a statement is represented by a node for the
subject, a node for the object, and a labeled arc between them for the
predicate. ... The examples also illustrate that RDF uses URIs as predicates
in RDF statements. "

Though the MT is clearer :

(0.2) "Finally, every arc in an RDF graph is labelled with a uriref. The
same uriref may label several arcs and also be a node in the graph"

So what this boils down to then (correct me if I'm wrong), to make
assertions about a specific instance of a predicate, it's necessary to first
reify the particular statement that contains it (which I think Seth was
saying). But then I don't see how information added by this means can be
accessed without the reification, and hence what use it can be (how does an
implementation know when to reify?).

Any clarification on this would be appreciated.

>>
>> What I've got at the moment is something like this :
>>
>>    Identifiable (Temporal, Described)
>>        |
>>       Item
>>    /   |   \
>> Vertex Edge (Adjunct)
>>
>> Identifiable more or less corresponds to URI
>
>This is the problem, an "edge" is not a URI as opposed to vertices
>which are
>named by URIs.

Presumably the edge (==arc) can have as an attribute the URI of a property
(e.g. dc:creator), but that this wouldn't be unique. The edge itself would
have an identity status akin to that of bNodes, only existing in relation to
the nodes to which it is connected.
Is there any good reason within RDF MT why the edge shouldn't have it's own
(instance) URI?

Cheers,
Danny.
Received on Wednesday, 19 June 2002 07:22:23 GMT

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