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Re: Actions 211 and 212: proposed changes to the extensions of basic graph pattern matching

From: Andy Seaborne <andy.seaborne@talis.com>
Date: Mon, 12 Apr 2010 16:33:45 +0100
Message-ID: <4BC33D59.5050402@talis.com>
To: Birte Glimm <birte.glimm@comlab.ox.ac.uk>
CC: SPARQL Working Group <public-rdf-dawg@w3.org>


On 09/04/2010 4:27 PM, Birte Glimm wrote:
> Hi all,
> below are my suggested text changes for the conditions on extensions
> to basic graph pattern matching. This is to address my open actions
> 212 and 211.
>
> http://www.w3.org/2009/sparql/track/actions/212
> Propose change to unique specified extension criteria
>
>
> Old text:
>
> 1 -- The scoping graph, SG, corresponding to any consistent active
> graph AG is uniquely specified and is E-equivalent to AG.
>
> Proposed text:
>
> 1 -- The scoping graph, SG, corresponding to any consistent active
> graph AG is specified uniquely up to differences in the identity of
> blank nodes and is E-equivalent to AG.
>
> alternatively (uses RDF graph equivalence as also used in condition 4,
> see below):
>
> 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.

Either looks OK to me.

http://www.w3.org/TR/rdf-concepts/#section-graph-equality

> http://www.w3.org/2009/sparql/track/actions/211
> Email out the text change needed to weaken the finite answer criteria
> in SPARQL Query
>
> Old text:
>
> 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.
>
> The condition has actually two purposes. 1) The answer set must be
> uniquely specified (up to RDF graph equivalence, blank node renaming)
> and 2) the answer set must be finite. We want to keep the first part
> and weaken the second part.
>
> Propsed text:
>
> 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. The conditions SHOULD prevent trivial infinite
> answers such as those from axiomatic triples and infinite answers that
> just differ in the identity of blank nodes.
>
> Alternatively:
>
> 4 -- Each SPARQL extension must provide conditions on answer sets,
> which guarantee that the answers set for every BGP and AG is uniquely
> specified up to RDF graph equivalence. The conditions must
> prevent infinite answers from axiomatic triples and infinite answers
> that just differ in the identity of blank nodes.
>
>
> I prefer the first proposal. It uses should and mainly suggests which
> sources of infinity should at least be addressed.

The first is fine but "trivial" has both technical and non-technical 
senses.  Can we ask the entailment regime to define what "trivial" means 
for each regime?

 > 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. The conditions SHOULD prevent trivial infinite
 > answers such as those from axiomatic triples and infinite answers that
 > just differ in the identity of blank nodes.

Maybe:
"""
, and should provide further conditions to prevent trivial infinite 
answers as appropriate to the regime.
"""

	Andy
Received on Monday, 12 April 2010 15:34:22 GMT

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