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Re: ACTION-221 - Reformulate Condition 4

From: Andy Seaborne <andy.seaborne@talis.com>
Date: Thu, 22 Apr 2010 13:48:57 +0100
Message-ID: <4BD045B9.2070600@talis.com>
To: Birte Glimm <birte.glimm@comlab.ox.ac.uk>
CC: SPARQL Working Group <public-rdf-dawg@w3.org>
Reworded 1 and 4 now in the doc rq25.xml

	Andy

On 20/04/2010 3:47 PM, Birte Glimm wrote:
> 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 Ī¼ 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
>
>
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Received on Thursday, 22 April 2010 12:49:18 GMT

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