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Concise Bounded Descriptions, bnode closure, OWL, and FOAF like models

From: Patrick Stickler <patrick.stickler@nokia.com>
Date: Thu, 25 Mar 2004 18:39:43 +0200
Message-Id: <049B886F-7E7B-11D8-B3C8-000A95EAFCEA@nokia.com>
To: RDF Data Access Working Group <public-rdf-dawg@w3.org>


I've been pondering about the extraction of concise bounded descriptions
in the case of "bnode-centric" models such as FOAF, and believe that
OWL can provide a very elegant and simple solution to the 
"overgeneration"
of levels that will occur with the present RDF-only definition of
concise bounded descriptions.

Essentially, owl:InverseFunctionalProperty is employed to bound the 
depth of
descriptions, such that, for any bnode object, if there exist any 
statements
for which it is the subject and which employ properties of rdf:type
owl:InverseFunctionalProperty then those and only those statements are
included in the description and the recursion ends there.

This provides just enough information about the bnode denoted resource
for an agent to obtain a complete description of that uniquely 
identified
resource if necessary, in a system-independent manner (irrespective
of system-specific bnode labels). In fact, the "fragment description"
of the resource consisting of only its uniquely identifying properties
constitute a query template, which should result in a complete 
description
of that resource.

If no statement with an instance of owl:InverseFunctionalProperty exists
for the bnode, then recursion continues, adding all statements about the
bnode delimited resource to the description.

Now, for vocabularies for which there do not (yet) exist any OWL
ontology which specifies which properties are of rdf:type
owl:InverseFunctionalProperty, the ability to submit auxiliary
knowledge along with an RDF query really shines. If one knows they
are querying a knowledge base using a particular bnode-centric
vocabulary, they can include along with the query extra information
such as, e.g.

    ex:emailAddress rdf:type owl:InverseFunctionalProperty .

or

    blargh:employeeNumber rdf:type owl:InverseFunctionalProperty .

etc.

to be taken into account when executing the query, and thus bounding
the bnode closure in an effective manner.

In any case, one would *have* to continue recursion for bnode
denoted resources where no uniquely identifying properties are
evident, since otherwise, one is unnable to request a description of
that bnode denoted resource in a system-independent, portable manner
since bnode labels are system-dependent. So simply limiting the number
of levels is not an optimal solution.

This OWL augmented approach to generating concise bounded descriptions
at least helps to lessen the magnitude of the problem substantially
(and completely solves the problem for FOAF, which already defines
which properties are instances of owl:InverseFunctionalProperty).

Eh?

Patrick

--

Patrick Stickler
Nokia, Finland
patrick.stickler@nokia.com
Received on Friday, 26 March 2004 03:20:36 GMT

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