From SPARQL Working Group
Draft reply to: MS-5
Thank you for your comment about the SPARQL Entailment Regimes document.
The SPARQL Query conditions on extending the basic graph pattern matching mechanism [1,2] specify that the effect of a query on an inconsistent graph must be specified by each SPARQL extension. Thus, not talking about this is not an option. Furthermore, the SPARQL Query specification requires that entailment regimes should provide conditions to prevent trivial infinite solution multisets as appropriate to the regime. Note that this is already a weakend version of the conditions for SPARQL 1.0 , but changing conditions of existing specs is always difficult and completely dropping this requirement seems out of the question.
For the RDF-Based Semantics it is clear that a consistency check does not necessarily terminate, which is ok with the specification (e.g., one could terminate with a timeout). The WG has decided, however, that if a system detects an inconsistency at any point during query answering, that this should be communicated to the user. It is explicitly allowed to do this in the form of a warning, e.g., together with or after some answers. Thus, the specification, e.g., for the RDF-Based Semantics, allows for terminating a consistency check after a certain timeout and a conformant implementation is possible even for undecidable logics. The WG decided, therefore, not to make changes to the working draft.
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