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Re: RDF graph merging question

From: Jan Algermissen <jalgermissen@topicmapping.com>
Date: Tue, 17 Aug 2004 20:41:55 +0200
Message-ID: <41225173.CE996942@topicmapping.com>
To: Graham Klyne <GK@ninebynine.org>
CC: algermissen@acm.org, "www-rdf-interest@w3.org" <www-rdf-interest@w3.org>

Graham, Thomas,

thanks for the quick reply. Your clarifications are helping a lot.

Comments below.

Graham Klyne wrote:

> >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?
> Er, no.  See section 3.3.1 of the RDF semantics specification, particulatly
> the final couple of paragraphs:

> -- http://www.w3.org/TR/2004/REC-rdf-mt-20040210/#Reif
> Which effectively says that separate nodes must be maintained for each
> reification that appears.

Just to confirm: this means, that gathering separate nodes that actually
represent the same 'thing' remains the burdon of the user of RDF (e.g.
at the query-formulation-level), right?

Example: Suppose two computers are connected and we represent this as

  foo:host1 bar:connectedTo foo:host2

Now, in RDF graph A the triple is reified to attach the information

  foo:conn-host1-host2 baz:connectionType foo:ethernet to it

(the connection is an ethernet connection)

Now in some strore B, the same triple exists and is reified to attach
a cable number:

  foo:connection-123 baz:cableNumber "XY-T-5665"

An RDF store (at least one that does not provide some non-standard
extension) cannot by itself provide me with the information that
the connection is of type ethernet and has cable number "XY-T-5665",

It would be the burdon of the one formulating the query to traverse all
the rdf:subject, rdf:predicate and rdf:object arcs to find the two
seperate nodes for what is actually a single 'thing'.

Is that true? Or am I approaching this in a completely wrong way?

> ... so there's no conflict to resolve.

Yes, appearently not ;-) 

In case it seemed so: my intention was not to point out a conflict, but
I am evaluating several data models for their suitability for data integration
and the issues above are my primary interest.

Thanks again.


Jan Algermissen                           http://www.topicmapping.com
Consultant & Programmer	                  http://www.gooseworks.org
Received on Tuesday, 17 August 2004 18:40:22 UTC

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