W3C home > Mailing lists > Public > public-rdf-dawg-comments@w3.org > August 2006

Re: What is "the serious bug in entailment semantics" found by J.Perez"?

From: Pat Hayes <phayes@ihmc.us>
Date: Fri, 11 Aug 2006 11:44:33 -0700
Message-Id: <p06230930c1027a5cc634@[]>
To: Jorge Pérez <jperez@ing.puc.cl>
Cc: franconi@inf.unibz.it, public-rdf-dawg-comments@w3.org

>Pat Hayes wrote:
>>  [Later: And the other example in
>>  http://lists.w3.org/Archives/Public/public-rdf-dawg-comments/2006Aug/0005
>>  makes the basic point more effectively.]
>>  However, consider the following example: same query, but against the graph
>>  {(a p a) (X p X) (X p b) }
>>  Here, I suggest, the answers ?q->a, ?q->X would
>>  be correct, in spite of the apparent redundancy,
>>  because the third triple clearly distinguishes
>>  (what is known about) X from (what is known
>>  about) a; so the redundancy is indeed only
>>  apparent.
>I totally agree with you that the answer ?q->a, ?q->X is correct in this
>case, but I think that your example is not related to the core of this

I agree, but I wanted to make this second point in order to head off 
some possible alternative suggestions for how to fix the bug which 
you identified.

>The "bug" in BGP E-matching is originated by redundancy in the
>dataset side (and queries about such redundancies) and has nothing to do
>with redundancy in the answer side, that (as your example shows) one not
>always want to eliminate.

Quite. This point has been contentious in the past, hence my example. 
I am glad we are in agreement on the correct behavior in these cases.

>Your example is "a good example" for the definitions, the dataset has no
>redundancy and the BGP E-matching definition (with simple entailment)
>gives the same solutions as the subgraph matching approach, so the "bug"
>is not present. Indeed, I think that it is a theorem that in the case of
>lean datasets the two approaches are always equivalent.

I also think this, but I no longer have total trust in my intuitions :-) .

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Received on Friday, 11 August 2006 18:44:45 UTC

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