- From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
- Date: Wed, 24 Sep 2008 10:04:37 -0400 (EDT)
- To: public-owl-wg@w3.org
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 14:05:23 UTC