Comparative preferences in sparql

Abstract

Sometimes one does not want all the solutions to a query but instead only those that are most desirable according to user-specified preferences. If a user-specified preference relation is acyclic then its specification and meaning are straightforward. In many settings, however, it is valuable to support preference relations that are not acyclic and that might not even be transitive, in which case though their handling involves some open questions. We discuss a definition of desired solutions for arbitrary preference relations and show its desirable properties. We modify a previous extension to SPARQL for simple preferences to correctly handle any preference relation and provide translations of this extension back into SPARQL that can compute the desired solutions for all preference relations that are acyclic or transitive. We also propose an additional extension that returns solutions at multiple levels of desirability, which adds additional expressiveness over prior work. However, for the latter we conjecture that an effective translation to a single (non-recursive) SPARQL query is not possible.