Querying Databases with Incomplete CP-nets

Preference queries aim to retrieve from large databases (DB’s) those objects that better match user’s requirements. With the aim of supporting modern DB applications, such as context-aware ones, in which conditional preferences are the rule, in this paper we investigate the possibility of adopting conditional preference networks (CP-nets) for DB querying. To this end, we also consider the relevant case in which CP-nets are not completely specified, a likely case for complex DB scenarios. We first show that the ceteris paribus (all else being equal) semantics, commonly associated with CP-nets, can lead to counterintuitive results if the CP-net is incomplete and the DB is incomplete as well. Then, we introduce a new totalitarian (i.e., not ceteris paribus) semantics and, rather surprisingly, prove that our semantics is equivalent to ceteris paribus for complete acyclic CP-nets and that yields the same optimal results if the DB is complete. Finally, we show that when both the CP-net and the underlying DB are incomplete the totalitarian semantics can lead to more accurate and intuitive results.