CommentResponse:AZ-1

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Dear Antoine,

thank you for the very detailed review.

You suggested to put Subsections 2.1 and 3.2 into a common Section. We have taken that advice an introduced a new (informative) section after the RDF entailment regime that contains discussions that are relevant to all regimes. In addition to the subsections you mentioned, the new section also contains the former subsections 2.2 to 2.4, which equally are not specific to the RDF regime.

You asked why D-entailment is not defined as in RDF Semantics or RIF/OWL. The definition of D-entailment does not prescribe the support of any datatypes, which means that without a minimally required datatype map, the D-entailment regime does not guarantee anything beyond the RDFS regime. Thus, the working group decided to specify a datatype map that has to be supported, which is a subset of the datatypes that RIF requires, but which omits less frequently used types (e.g., xsd:hexBinary or xsd:NMTOKEN). Systems can always go the extra mile and also support the less common dataypes. Apart from xsd:date and xsd:time, the chosen datatype map is also a subset of the OWL RL and, hence, the OWL datatype map in general. We believe, however, that xsd:date and xsd:time are so popular that a lack of support for them seems problematic.

The detailed comments have mostly been addressed in the proposed way. The point that has not been addressed exactly as suggested is the following:

- Sec.5.3: "reasoning problems in OWL under OWL 2 RDF-Based Semantics
  are undecidable ..." -> semi decidable, which means the computation
  of the query results always finishes in finite time.

The terminology has been changed to semidecidable, which is more precise than undecidable, but that still does not mean that the computation of the query results always finishes in finite time.

The reasoning problems are semidecidable, i.e., positive entailments can be enumerated whereas for negative entailments (non-consequences of the ontology) the reasoner might not come back with the answer in finite time (semidecidable). If we were to find the answers to { ?x rdfs:subClassOf ex:C } w.r.t. an OWL Ful ontology, then any binding for ?x that instantiates the triple into a non-entailed subsumption might cause the reasoner to not come back with an answer in finite time, whereas for bindings that instantiate the triple into an entailed subsumption, there is a (theoretical) guarantee that the reasoner comes back after finitely many steps with the answer. Now what one can do in practise if of course to give a time limit to the reasoner and only the answers that can be found in the time limit are returned. In that case we might miss some positive entailments, which could not be determined in the given time limit. Hence, we possibly get incomplete answers.

We hope that this answer adresses your concerns. The updated working draft is available at: http://www.w3.org/2009/sparql/docs/entailment/xmlspec.xml

We would be grateful if you would acknowledge that your comment has been answered by sending a reply to this mailing list.

Birte (on behalf of the SPARQL WG)