Bronze from anear, by gold from afar? points to Semantic Web Architecture: Stack or Two Towers? "Features such as closed world assumption and negation as failure (NAF) can be supported by powerful query languages—queries already have a closed world flavour (because distinguished variables can only bind to named individuals), and it is natural to extend this with NAF by way of query subtraction (e.g., the answer to the query “faculty(?x) and NAF professor(?x)” can be computed by subtracting the answer to the query “professor(?x)” from the answer to the query “faculty(?x)”). These features are already supported in query languages such as SPARQL  and nRQL  (the query language implemented in the Racer system). Moreover, recent work on integrating rules with OWL suggests that future versions of this framework could include, e.g., a decidable subset of SWRL, and a principled integration of OWL and Answer Set Programming [5, 12, 13].
On the other hand, adopting Datalog rules (and DLP with Datalog semantics) would effectively establish two Semantic Webs, with little or no semantic interoperability between the rules based Semantic Web and the ontology based Semantic Web, even at the RDF level. These two versions of the Semantic Web would inevitably be in competition with each other, and this would make the Semantic Web much less appealing: new users would be presented with a difficult choice as to which part to choose, and in choosing would sacrifice semantic interoperability with the other part."