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Re: LC Comment on Entailment Regimes: Insufficient Definition of "Entailment Regime"

From: Birte Glimm <birte.glimm@uni-ulm.de>
Date: Thu, 10 Nov 2011 10:19:46 +0100
Message-ID: <CABt65OcXF8MpDpp+4cSOqjBfcyvzOd8LSAcNYs1q5H_U3-WntA@mail.gmail.com>
To: Michael Schneider <schneid@fzi.de>
Cc: public-rdf-dawg-comments@w3.org
Michael,

I reply again, this time putting the comments mailing list in cc.

Thank you for your comment about the SPARQL Entailment Regimes document.

The conditions for extensions of basic graph pattern matching have
already been defined in the SPARQL 1.0 query document and are not part
of the current specification (see Section 12.6:
http://www.w3.org/TR/rdf-sparql-query/#sparqlBGPExtend). The
conditions do not exclude, however, the possibility of defining only
certain basic graph patterns (which are not necessarily RDF graphs as
they can contain variables) as well-formed for the regime.

The OWL Direct Semantics regime in particular makes use of this since
it only accepts well-formed BGPs that can be parsed into OWL
structural objects extended to allow for variables as described in the
spec. The regime even defines further conditions, notably (C3), that
make sure that the union of the queried ontology and an instantiated
BGP satisfy the OWL 2 DL constraints. Your given example query would
be illegal for the Direct Semantics regime as it violates condition
(C3) of the regime.

We hope that this reply addresses your comment and would be grateful
if you would acknowledge this by sending a reply to this mailing list.

Birte, on behalf of the SPARQL-WG

On 26 July 2011 14:03, Michael Schneider <schneid@fzi.de> wrote:
> Dear all!
>
> Document: SPARQL 1.1 Entailment Regimes
> State: LCWD
>
> In Section 1.3, condition 1, the specification of "entailment regimes"
> states:
>
>    1. A subset of RDF graphs called well-formed
>       for the regime
>
> I believe that this condition is not sufficient for all entailment regimes
> in the document.
>
> Rational:
> ---------
>
> Take, for example, the following queried graph O and the (ground) BGP O1:
>
>    O = {
>        :p rdf:type owl:TransitiveProperty .
>    }
>
>    O1 = {
>        :p rdf:type owl:AsymmetricObjectProperty .
>    }
>
> Under the OWL 2 DL syntax [1], both O and O1 are syntactically valid
> ontologies (in RDF graph form), so they meet condition 1 for the OWL 2
> Direct Semantics Entailment Regime. However, the entailment query "(O, O1)"
> is /not/ valid, as the combination of both graphs hurts the global
> restrictions in Chap. 11 of [1]: transitive properties must not be
> asymmetric properties. This is explained at the end of Chap. 3 of [2]:
>
>    For ontology equivalence to be decidable,
>    O1 needs to satisfy this restriction w.r.t.
>    O and vice versa.
>
> (I believe that this condition of the Direct Semantics should not be
> restricted to /equivalence/, but is also needed for entailment).
>
> So, I believe that a entailment query "(O, O1)" has to be disallowed for the
> OWL 2 Direct Entailment Regime, at least if this regime is restricted to the
> OWL 2 DL syntactic fragment of OWL 2.
>
> Proposal:
> ---------
>
> Instead, I suggest, to change the condition as follows:
>
>    1. A set of /pairs of RDF graphs/ called well-formed
>       for the regime
>
> In addition, in the tables for all entailment regimes, the row "Legal
> Graphs" should be replaced by "Legal Graph Pairs" or something like "Legal
> Entailment Queries", with the corresponding texts being updated.
>
> Final Note:
> -----------
>
> If, against my current understanding, the OWL 2 Direct Entailment Regime is
> meant to be applicable to the full OWL 2 Structural Specification [1], and
> not only to the OWL 2 DL fragment with the global constraints to retain
> decidability (and other restrictions), then my comment is moot. But then,
> the document should be carefully checked that there is really no dependency
> on the OWL 2 DL fragment anywhere else.
>
> [1] http://www.w3.org/TR/2009/REC-owl2-syntax-20091027/
> [2] http://www.w3.org/TR/2009/REC-owl2-direct-semantics-20091027/
>
> Best regards,
> Michael
>
> --
> Dipl.-Inform. Michael Schneider
> Research Scientist, Information Process Engineering (IPE)
> Tel  : +49-721-9654-726
> Fax  : +49-721-9654-727
> Email: michael.schneider@fzi.de
> WWW  : http://www.fzi.de/michael.schneider
> ==============================================================================
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> Haid-und-Neu-Str. 10-14, D-76131 Karlsruhe
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> Studer
> Vorsitzender des Kuratoriums: Ministerialdirigent Günther Leßnerkraus
> ==============================================================================
>
>



-- 
Jun. Prof. Dr. Birte Glimm            Tel.:    +49 731 50 24125
Inst. of Artificial Intelligence         Secr:  +49 731 50 24258
University of Ulm                         Fax:   +49 731 50 24188
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Received on Thursday, 10 November 2011 09:20:27 GMT

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