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Re: wording on Unknown returns in Conformance

From: Alan Ruttenberg <alanruttenberg@gmail.com>
Date: Wed, 24 Sep 2008 12:17:07 -0400
Message-ID: <29af5e2d0809240917w49d02203ke989ad35ed81ea4d@mail.gmail.com>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
Cc: public-owl-wg@w3.org

I had thought that it might be worth distinguishing distinct levels of
conformance - complete versus incomplete. Do you think that would be a
good idea? It bothers me a bit that conformance as specified for OWL
Full, as stated now, is not known to be possible.
-Alan


On Wed, Sep 24, 2008 at 10:04 AM, Peter F. Patel-Schneider
<pfps@research.bell-labs.com> wrote:
>
> There have been some comments on the "should not" wording in the
> conformance part of the Test and Conformance document.
>
> The current wording includes
>
>  An OWL 2 Full entailment checker is an OWL 2 entailment checker that
>  takes RDF documents as input, and uses the RDF-Based Semantics [OWL 2
>  RDF-Based Semantics]. It MUST return True only when O1 entails O2, and
>  it MUST return False only when O1 does not entail O2. It SHOULD NOT
>  return Unknown.
>
> Without the last sentence, a trivial checker, i.e., one that always
> returned "Unknown" would be just as good an OWL 2 Full entailment
> checker as one that tried hard.
>
> Even worse, if the last sentence was removed from
>
>  An OWL 2 DL entailment checker is an OWL 2 entailment checker that
>  takes OWL 2 DL ontology documents as input, and uses the Model
>  Theoretic Semantics [OWL 2 Semantics]. It MUST return True only when
>  O1 entails O2, and it MUST return False only when O1 does not entail
>  O2. It SHOULD NOT return Unknown.
>
> then a trivial checker would be just as good as a complete reasoner for
> OWL 2 DL.
>
>
> I thus feel that there needs to be some wording in the conformance
> document to show that trivial checkers, or unnecessarily incomplete
> checkers, are not as good as ones that return "Unknown" in fewer cases.
>
> Remember that "should not" is not the same as "must not".  A checker
> could return "Unknown" if
> 1/ it ran out of resources (memory, time, etc.); or
> 2/ it is an incomplete reasoner (for OWL 2 Full, for example, or even
>   for OWL 2 DL).
> The above reasons (or others) could be used by entailment checkers to
> provide a justification for "Unknown" answers.  I feel, however, that
> this is outside the scope of the specification.
>
> Perhaps it would be useful to add some wording on justifying "Unknown"
> to the document, but I think that most of this is implied by the use of
> "should not".
>
> peter
>
>
Received on Wednesday, 24 September 2008 16:17:47 UTC

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