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Re: Review of RIF Core entailment in SPARQL draft

From: Jos de Bruijn <jos.debruijn@gmail.com>
Date: Tue, 27 Jul 2010 17:34:57 +0200
Message-ID: <AANLkTimZj89N=DiZAVY6JcWKm2EPdX-av8FPgYsY1+qZ@mail.gmail.com>
To: Sandro Hawke <sandro@w3.org>
Cc: RIF <public-rif-wg@w3.org>
Ok, I sent the review directly to the dawg-comments list

On Tue, Jul 27, 2010 at 17:20, Sandro Hawke <sandro@w3.org> wrote:
> Jos, I think it makes sense to keep this more conversational, and have
> you directly reply with this, rather than us discuss it much internally
> first.   If you agree, please send this to
> public-rdf-dawg-comments@w3.org
>     -- Sandro
> On Mon, 2010-07-26 at 14:39 +0200, Jos de Bruijn wrote:
>> I reviewed the RIF Core entailment section of the current SPARQL 1.1
>> Entailment Regimes draft [1]. Find my comments below.
>> Major comment (section 7.2):
>> I did not understand the definition of Query Answers. It is unclear
>> what the combination is for which RIF-Simple entailment is checked. In
>> particular, which are the RDF graphs that are considered? Is this just
>> the scoping graph or also the graphs imported by the rule set (the
>> text in the "Legal Graphs" row seems to sanction such imports).
>> Errors:
>> - Sec 7, 2nd par, 1st sentence: the phrase "...satisfiability and
>> entailment, each of which define how a common RIF-RDF interpretation
>> is a model of a combination" is incorrect. Satisfiability defines when
>> (not how) an interpretation is a model; entailment does not define
>> models.
>> - Sec 7, 1st par::
>>    * It is claimed here that entailment is checked wrt. a
>> Skolemization of the scoping graph. This contradicts the definition of
>> query answers in Sec. 7.2.
>>    * It is claimed that only combinations with one RDF graph are
>> considered. This seems to contradict the definition of Legal Graphs in
>> Sec. 7.2.
>> - Sec 7.2, def query answers: rif:imports is not a predicate, it is a CURIE
>> - Sec 7.2, "RIF-Core conformance is defined with respect to safe rules
>> and so this entailment regime is defined with respect to combinations
>> formed from safe RIF documents.": Not true. This entailment regime is
>> defined with respect to safe RIF document because it is defined as
>> such, in the row "Legal Graphs" of the table.
>> - Sec 7.4, 2nd par: cyclic references *do not* rule out the existence
>> of a unique minimal model. I believe that every RIF Core document has
>> a single unique minimal Herbrand model. Strong safety can, in
>> addition, guarantee finiteness (when not considering the datatypes).
>> - Sec 7.4, 3rd par: RIF models are necessarily infinite, since the
>> domain includes includes all integers.
>> Further comments:
>> - Sec 7.2, 1st editorial note: I wanted to see if I can answer the
>> question, but could not find any definition of "answer set" in the
>> draft
>> - Sec 7.3: I do not understand the relation between the text in this
>> section and RIF Core entailment in SPARQL. I see implementation hints
>> about RDFS and OWL 2 RL; it seems to me these hints should be included
>> in the respective RDFS and OWL 2 RL sections.
>> - Sec 7.4, 2nd sentence: I cannot parse '(with possibly infinite)'.
>> - Sec 7.4, 2nd par: it is not clear why stratification is discussed
>> here, since RIF Core has not negation. In general, I find the
>> paragraph a bit confusing. I think it should be rewritten.
>> Discussion points:
>> - I would suggest to remove the rif:imports triple from the scoping
>> graph, since it may lead to unexpected inferences.
>> [1] http://www.w3.org/TR/sparql11-entailment/#id35811294

Jos de Bruijn
  Web:          http://www.debruijn.net/
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Received on Tuesday, 27 July 2010 15:43:08 UTC

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