Re: named graphs and rdfg:subGraphOf

Ho,

we have also an ontology for that, NRL, which models importing of named
graphs into each other.
It is used in NEPOMUK.

http://www.semanticdesktop.org/ontologies/2007/08/15/nrl/

overview on importing graphs
http://www.semanticdesktop.org/ontologies/2007/08/15/nrl/#mozTocId929002

subGraphOf:
http://www.semanticdesktop.org/ontologies/2007/08/15/nrl/#mozTocId178125

there are some experimental implementations:
https://dev.nepomuk.semanticdesktop.org/wiki/NrlValidator
https://dev.nepomuk.semanticdesktop.org/wiki/NRLSail
(second for sesame)

there are also some publications, google should find them.

note that the popular NIE ontologies (used in Nepomuk.kde.org) are built
on top of NRL, so NRL is in production on many linux desktop search
engines in KDE.

best
Leo

It was Steffen Staab who said at the right time 08.10.2009 18:21 the
following words:
> Hi,
>
> you might want to take a look at networked graphs a declarative
> mechanism for describing relationships between graphs:
>
> there is a WWW paper:
> http://www.uni-koblenz.de/~staab/Research/Publications/2008/NetworkedGraphs-WWW2008.pdf
>
>
> an open source implementation on top of Sesame:
> http://isweb.uni-koblenz.de/Research/systeme/NetworkedGraphs
>
> and an example application:
> http://isweb.uni-koblenz.de/Research/systeme/semap
>
> Steffen
>
>
>
>
>
> Pat Hayes schrieb:
>>
>> On Oct 7, 2009, at 3:46 PM, Jakub Kotowski wrote:
>>
>>> Hello,
>>>
>>> I am trying to understand the definition of the rdfg:subGraphOf
>>> property
>>> from [1,2]. It says that:
>>>
>>> <f,g> is in IEXT(I(rdfg:subGraphOf))  iff
>>> rdfgraph(f) is a subset of rdfgraph(g)
>>>
>>>
>>> What confuses me is probably the "syntactic part" of the definition:
>>> rdfgraph(f) is the ("syntactical") set of triples of the named graph f.
>>
>> Yes, graphs are indeed syntactic entities.
>>
>>> I am wondering whether it means that if rdfgraph(g) does not contain
>>> all
>>> the triples from rdfgraph(f) I can infer them - so that after the
>>> inference proces I'll get a new, enriched rdfgraph(g) for which the
>>> condition already holds (rdfgraph(f) is a subset of rdfgraph(g))...?
>>
>> It was not intended to have this kind of 'procedural' interpretation,
>> but if you had a system which tried to generate graphs from their
>> descriptions, then this might make sense. It would not be inference,
>> however, but something more like a graph construction process.
>>
>>> Instead of this description I would almost rather like to ask
>>> whether it
>>> means that the triple f rdfg:subGraphOf g entails:
>>> g {
>>>     rdfgraph(f)
>>>     plus whatever was in g before
>>
>> Before what, exactly? You seem to have a process or procedure in
>> mind, but I do not follow what it is. The rdfg vocabulary is intended
>> for describing relationships between graphs which already exist.
>>
>>> }
>>> But that doesn't seem to be correct because entailment is not defined
>>> over a set of named graphs.
>>>
>>> The alternative would be that a knowledge base containing:
>>>     the triple        f rdfg:subGraphOf g
>>>     the named graph        f
>>>     the named graph        g ...(the original, not enriched one)
>>>
>>> is inconsistent because rdfgraph(f) is not a subset of rdfgraph(g) but
>>> the triple f rdfg:subGraphOf g is asserted.
>>
>> Well, indeed, this combination as described is inconsistent. Now the
>> question is, what to do about this inconsistency when it has been
>> detected, if anything. One possibility is simply to report it as an
>> inconsistency. Another is to try to 'repair' it, by changing the
>> world so as to make it consistent. This could be done in various
>> ways: the subgraph assertion could be rejected, for example, or the
>> graph named g could be expanded to include the triples of the graph
>> f. The formal semantics does not specify which of these, if any, is
>> correct or appropriate: it simply specifies the inconsistency. What
>> can be done depends in practice largely on who has ownership of the
>> various graphs involved.
>>
>>> Well, this alternative maybe
>>> does not even make sense because a set of (accepted) named graphs is
>>> defined to have the usual RDF semantics of the merge of the respective
>>> graphs.
>>>
>>> On the one hand the first interpretation would seem more plausible
>>> because it would make the rdfg:subGraphOf property usable as a way of
>>> nesting named graphs, on the other hand, the provenance motivation for
>>> named graphs seems to be in favour of the alternative interpretation
>>> which sees the property as rather descriptive.
>>
>> Certainly, the property is intended to be purely descriptive, as far
>> as the normative specification is concerned.
>>
>>> After all, if a graph
>>> changes because of inference (inferred triples are added) then the new
>>> graph should probably be associated with provenance information which
>>> documents that it was inferred and possibly how.
>>
>> Certainly it will be a different graph, one with a different name.
>> Named graphs are not intended to be names of *dynamic* graphs. The
>> usual rules of 'cool URI' usage apply here just as they would to any
>> other document or information resource.
>>
>>>
>>> At least the following is true, right?
>>>
>>> :f rdfg:subGraphOf :g does not hold if :f and :g are specified as
>>> follows:
>>>
>>> :f {
>>>     :a rdfs:subclassOf :c .
>>> }
>>>
>>> :g {
>>>     :a rdfs:subclassOf :b .
>>>     :b rdfs:subclassOf :c .
>>> }
>>>
>>
>> That is correct. In this case f is a subgraph of the RDFS closure of
>> g, but not of g itself.
>>
>> Hope this helps.
>>
>> Pat Hayes
>>
>>> Am I just making things too complicated and overlooking something?
>>> By the way, esentially this question has already been asked but
>>> unfortunately left unanswered:
>>> http://lists.w3.org/Archives/Public/semantic-web/2006May/0108.html
>>>
>>> Best regards,
>>> Jakub Kotowski
>>>
>>>
>>> [1] Named graphs, provenance and trust Export
>>> Jeremy J. Carroll, Christian Bizer, Pat Hayes, Patrick Stickler
>>> In WWW '05: Proceedings of the 14th international conference on World
>>> Wide Web (2005), pp. 613-622.
>>>
>>> [2] Named graphs
>>> J. Carroll, C. Bizer, P. Hayes, P. Stickler
>>> Web Semantics: Science, Services and Agents on the World Wide Web In
>>> World Wide Web Conference 2005------Semantic Web Track, Vol. 3, No. 4.
>>> (December 2005), pp. 247-267.
>>>
>>>
>>>
>>
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>>
>>
>>
>>
>>
>>
>


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Received on Monday, 12 October 2009 10:11:50 UTC