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Re: Reification and Provenance modelling

From: Ivan Herman <ivan@w3.org>
Date: Mon, 31 Jan 2011 10:37:37 +0100
Cc: public-rdf-comment@w3.org, W3C Chairs of the RDF WG <team-rdf-chairs@w3.org>
Message-Id: <162BAACE-70E0-47FE-B138-BD7E81FEEB77@w3.org>
To: Bob Ferris <zazi@elbklang.net>

this is not a technical but rather a more administrative response...

The RDF WG is, currently, only gathering. What this means in practice is that people are signing up to the group and the real work will begin mid-February. In the meantime, I have archived this mail so that it could be put 'back' into the collective psyche of the group when the time comes...


On Jan 28, 2011, at 20:18 , Bob Ferris wrote:

> Hi,
> since the new RDF WG is still forming, I thought it might be worth to bring up two issues re. reification and provenance modelling in here.
> 1. As I saw one issue on the new agenda is the standardization of the meaning of the forth element in quadruples. There might be a tendency that this should be used for referring the URI of a "named graph" (a set of triples, that means, hopefully more than one).
> However, currently I would rather tend to assign the forth element for an optional statement identifier, which is explicitly intended to be used for addressing provenance information. Provenance information is from my point of view 'external context' (cf. [1]) to information described in a semantic graph.
> The following example is also a response[2] of the question of how to do practical Named Graphs implementations[3]:
> This design allows triple (statement) identification over the enclosures of named semantic graphs and furthermore the treatment of provenance for statements and graphs in a same way. Additionally, the handling of n-ary relations, as an 'internal context' (cf. [1]) refinement of binary relation based descriptions, and its mapping to binary relations (property reification, see [4]).
> Here is an example, which was original only intended for representing the internal structure of a quad store. However this could also be used in a serialization format (cf. N-Quads [5], where the forth element is also optionally). I reformatted it to an N-Quad like serialization:
> <#alice> :friend <#bob> <#s1> . # a simple binary relation
> <#ab> rdf:type :HumanRelationship <#s2> ; # a property reification (an n-ary relation) related to the first binary relation
> <#ab> :participant <#alice> <#s3> ;
> <#ab> :participant <#bob> <#s4> ;
> <#ab> :relationshipType :friend <#s5> ;
> <#ab> :since "2010-12-12"^xsd:date <#s6> .
> <#s1> :reified <#ab> <#s7> ; # an inference that results in a reification relation (such a property currently does not exist, or?)
> <#g1> rdf:type rdfg:Graph <#s8> ; # a graph enclosure (which can also be more nicely serialized by the TriG syntax)
> <#g1> :contains <#s1> <s#9> ;
> <#g1> :contains <#s2> <#s10> ;
> <#g1> :contains <#s3> <#s11> ;
> <#g1> :contains <#s4> <#s12> ;
> <#g1> :contains <#s5> <#s13> ;
> <#g1> :contains <#s6> <#s14> ;
> <#g1> :contains <#s7> <#s15> .
> <#g2> rdf:type rdfg:Graph <#s16> ; # another graph enclosure
> <#g2> :contains <#s1> <#s17> .
> -> I can easily get all statements of a graph by using the :contains relation (indexing)
> -> I can easily get semantically related property-oriented context descriptions (n-ary relations) by using the :reified relation
> -> provenance on the statement and on the graph level can easily be done by describing the <#g*> and <#s*> information resources:
> - thereby, <#s9> - <s#15> and <s#17> are intended for describing provenance information of statement <#s*> in graph <#g*>
> - one can maybe also inherit graph based provenance information to statement provenance information (and vice versa)
> -> one can also decouple a reused statement by changing its statement identifier; that means, the triple of the statement are still the same but the relation to the original statement might now be another e.g., reflected by a provenance statement e.g., <#s20> :original <#s19>
> -> statement descriptions can be typed i.e. by rdf:Statement (maybe obsolete now, since the new agenda propagates a deprecation of the RDF Reification vocabulary)
> Can such a storing be efficient for the intended use case (practical Named Graph implementation)?
> 2. As one can see already in the first example the application of property reification, the Property Reification Vocabulary [4] is intended for describing the definitions of such mappings on the vocabulary level. So, a reasoning engine can apply the two rules of the Property Reification Vocabulary, the shortcut relation rule[6] and the property reification rule[7], to infer that a binary relation particular and a reification class particular belonging semantically together.
> A property reification definition for the example above, would look like the following one:
> ex:FriendReification a prv:PropertyReification ;
>   prv:shortcut :friend ;
>   prv:shortcut_property :relationshipType ;
>   prv:reification_class :HumanRelationship ;
>   prv:subject_property :participant ;
>   prv:object_property :participant .
> In this case the :friend relation would also be a symmetric relation.
> A mapping (inference) of reification class particular descriptions to the RDF Reification vocabulary can be done. However, I'm unsure, whether this is really necessary.
> Finally, I think we have to differ somehow the modelling of 'internal' and 'external context'. The modelling of 'internal context' (refinements) would still be on the same level as the usual modelling of binary relations. The modelling of 'external context' (i.e. provenance and trust) would be shifted on another level.
> Any comments, suggestions, questions and critics are very welcome.
> Cheers,
> Bob
> [1] http://www.dbis.informatik.uni-frankfurt.de/~tolle/Publications/2004/AISTA04.pdf
> [2] http://blog.dbtune.org/post/2010/12/21/Named-Graphs-and-implementations#c9094397
> [3] http://blog.dbtune.org/post/2010/12/21/Named-Graphs-and-implementations
> [4] http://purl.org/ontology/prv/core#
> [5] http://sw.deri.org/2008/07/n-quads/
> [6] http://smiy.sourceforge.net/prv/rdf/shortcut_relation_rule.n3
> [7] http://smiy.sourceforge.net/prv/rdf/property_reification_rule.n3

Ivan Herman, W3C Semantic Web Activity Lead
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Received on Monday, 31 January 2011 09:37:28 UTC

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