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RDF graph merging question

From: Jan Algermissen <jalgermissen@topicmapping.com>
Date: Tue, 17 Aug 2004 15:12:49 +0200
Message-ID: <41220451.937058CF@topicmapping.com>
To: "www-rdf-interest@w3.org" <www-rdf-interest@w3.org>

Hi,

I have a question regarding the merging of RDF graphs, that contain
reified statements.

I am using the example[1] from the RDF Primer.

Suppose I have RDF graph A containing the following set of triples:

exproducts:triple12345   rdf:type        rdf:Statement .
exproducts:triple12345   rdf:subject     exproducts:item10245 .
exproducts:triple12345   rdf:predicate   exterms:weight . 
exproducts:triple12345   rdf:object      "2.4"^^xsd:decimal .

Now, assume I also have a graph B, containing the following set:

foo:bar   rdf:type        rdf:Statement .
foo:bar   rdf:subject     exproducts:item10245 .
foo:bar   rdf:predicate   exterms:weight . 
foo:bar   rdf:object      "2.4"^^xsd:decimal .

In my understanding the semantics of rdf:subject, rdf:predicate and
rdf:property allow to conclude that the two reified statements are the
same statement and should be represented as a single node in the
resulting merged RDF graph.

Correct?

But then, since the statements have been assigned different URIs (by
the different authors of the two graphs) it is not possible to
actually perform the merge, since RDF graphs only allow a single URI
per node.

Correct?


Now, assume the assigned URIs mactch, but the objects are different:

exproducts:triple12345   rdf:type        rdf:Statement .
exproducts:triple12345   rdf:subject     exproducts:item10245 .
exproducts:triple12345   rdf:predicate   exterms:weight . 
exproducts:triple12345   rdf:object      "2.4"^^xsd:decimal .

and

exproducts:triple12345   rdf:type        rdf:Statement .
exproducts:triple12345   rdf:subject     exproducts:item10245 .
exproducts:triple12345   rdf:predicate   exterms:weight . 
exproducts:triple12345   rdf:object      "117.89"^^xsd:decimal .

Now the assigned URI demands the merge, but the semantics of rdf:subject,
rdf:predicate and rdf:property tell us, that there are really two different
statements.

What happens during the merge?


Note that the underlying issue is, if the combination of rdf:subject,
rdf:predicate and rdf:property is identity-providing and if so, how
this means of identity-providing relates to the URI-means of providing
identity. Is one stronger than the other? Etc...


Is there any material on the Web, that addresses these kinds of issues
when merging RDF graphs?

I would really apprechiate if someone could shed some light on these
issues, thanks a lot in advance.


Jan

[1] http://www.w3.org/TR/rdf-primer/#reification

-- 
Jan Algermissen                           http://www.topicmapping.com
Consultant & Programmer	                  http://www.gooseworks.org
Received on Tuesday, 17 August 2004 13:11:11 UTC

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