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RE: ACTION-221 - Reformulate Condition 4

From: Birte Glimm <birte.glimm@comlab.ox.ac.uk>
Date: Tue, 20 Apr 2010 15:47:15 +0100
Message-ID: <m2x492f2b0b1004200747ic3d0ace2u8d6078b504d36fe7@mail.gmail.com>
To: Axel Polleres <axel.polleres@deri.org>, SPARQL Working Group <public-rdf-dawg@w3.org>
Here's my new attempt to rephrase condition 4, so that RDF graph
equivalence for answers is hopefully clarified.

Here's the original condition:

4 -- Each SPARQL extension MUST provide conditions, which guarantee
     that the answer set for every BGP and AG is uniquely specified up to
     RDF graph equivalence, and SHOULD provide further conditions to
     prevent trivial infinite answers as appropriate to the regime.

Here's the proposed change:

4 -- Each SPARQL extension MUST provide conditions, which guarantee
      that the set of triples obtained by instantiating BGP with each
      solution μ is uniquely specified up to RDF graph equivalence, and
      SHOULD provide further conditions to prevent trivial infinite answers
      as appropriate to the regime.

Birte
On 20 April 2010 14:27, Axel Polleres <axel.polleres@deri.org> wrote:
> I am fine with the Condition 1 rewording...
>
> As for 4:
>> 4 -- Each SPARQL extension MUST provide conditions, which guarantee
>>      that the answer set for every BGP and AG is uniquely specified up to
>>      RDF graph equivalence, and SHOULD provide further conditions to
>>      prevent trivial infinite answers as appropriate to the regime.
>
>
> 1) I have a problem with the first part (which actually comes from the original condition 4)
>
> "that the answer set for every BGP and AG is uniquely specified up to RDF graph equivalence,"
>
> Can someone tell me what "unique up to RDF graph equivalence" for an answer set actually means?
> RDF graph equivalence is only defined for RDF Graphs, or no? Can't this in the light of Condition 1 just
> be dropped?
>
> 2) I am fine with the remaining part:
>
> "and SHOULD provide further conditions to prevent trivial infinite answers as appropriate to the regime."
>
> Just as an example, why we may be careful with the previous wording suggestion referring to axiomatic triples:
> as to what means "prevent infinite answers from axiomatic triples..."?
>
> e.g.
>
> 1) Is this following infinity "from axiomatic triples"?
>
> Entailment: RIF + RDFS
>
> Graph:
>
> {}
>
> RIF ruleset:
>
>  ?X :q 1 :-  ?X a rdf:type rdfs:Datatype .
>  ?X :q External( ?Y + 1 ):-  ?X :q ?Y
>  ?Z rdf:type :c  :- And( ?X :q ?Y
>                         External( pred:iri-string( ?Z concat("rdf:_" ?Y) )))
>
> Query:
>
> SELECT ?X WHERE { ?X rdf:type :c }
>
> Answer:
>  rdf:_1
>  rdf:_2
>  ...
>
> Answer:
>
>
> 2) Is this following infinity "from axiomatic triples"?
>
> Entailment: RDFS
>
> Graph:
>  rdfs:ContainerMembershipProperty rdfs:subClassOf :c
>
> Query:
>
> SELECT ?X WHERE { ?X rdf:type :c }
>
> Answer:
>  rdf:_1
>  rdf:_2
>  ...
>
> best,
> Axel
>
> On 19 Apr 2010, at 11:46, Birte Glimm wrote:
>
>> Hi all,
>> following up on the proposed changes to the extensions of BGP
>> matching, I would suggest the following. The first condition is
>> changed from
>> 1 -- The scoping graph, SG, corresponding to any consistent active
>>       graph AG is uniquely specified and is E-equivalent to AG.
>> to
>> 1 -- The scoping graph, SG, corresponding to any consistent active
>>       graph AG is specified uniquely up to RDF graph equivalence and is
>>       E-equivalent to AG.
>> Then we have made it explicit that differences in bnode labels only are ok.
>>
>> The second change regarding finiteness is more tricky. I'll try what
>> Andy suggested, which leaves it to the entailment regimes to identify
>> appropriate conditions and suggest to change from
>> 4 -- Each SPARQL extension must provide conditions on answer sets
>>      which guarantee that every BGP and AG has a finite set of answers
>>      which is unique up to RDF graph equivalence.
>> to
>> 4 -- Each SPARQL extension MUST provide conditions, which guarantee
>>      that the answer set for every BGP and AG is uniquely specified up to
>>      RDF graph equivalence, and SHOULD provide further conditions to
>>      prevent trivial infinite answers as appropriate to the regime.
>>
>> Maybe we can discuss and hopefully agree on that in tomorrow's teleconf.
>> Cheers,
>> Birte
>>
>>
>> --
>> Dr. Birte Glimm, Room 306
>> Computing Laboratory
>> Parks Road
>> Oxford
>> OX1 3QD
>> United Kingdom
>> +44 (0)1865 283529
>>
>>
>
>



-- 
Dr. Birte Glimm, Room 306
Computing Laboratory
Parks Road
Oxford
OX1 3QD
United Kingdom
+44 (0)1865 283529
Received on Tuesday, 20 April 2010 14:47:53 GMT

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