From SPARQL Working Group
Draft reply to: MS-3
Thank you for your comment about the SPARQL Entailment Regimes document.
The conditions for extensions of basic graph pattern matching have already been defined in the SPARQL 1.0 query document and are not part of the current specification (see Section 12.6: http://www.w3.org/TR/rdf-sparql-query/#sparqlBGPExtend). The conditions do not exclude, however, the possibility of defining only certain basic graph patterns (which are not necessarily RDF graphs as they can contain variables) as well-formed for the regime.
The OWL Direct Semantics regime in particular makes use of this since it only accepts well-formed BGPs that can be parsed into OWL structural objects extended to allow for variables as described in the spec. The regime even defines further conditions, notably (C3), that make sure that the union of the queried ontology and an instantiated BGP satisfy the OWL 2 DL constraints. Your given example query would be illegal for the Direct Semantics regime as it violates condition (C3) of the regime.
We hope that this reply addresses your comment and would be grateful if you would acknowledge this by sending a reply to this mailing list.
Birte, on behalf of the SPARQL-WG