Providing semantic intelligent answers to recursive queries

We study the issue of providing intelligent answers to recursive queries. We first extend the notion of intelligent answers by allowing them to be incomplete. Complete and incomplete intelligent answers are both useful in that they provide (possibly partial) characterizations of queries for users to understand. Complete intelligent answers also allows us to compute the queries more efficiently. We propose a general approach that enables us to combine several cases studied previously for constructing intelligent answers, Moreover, in our approach, semantic constraints can be systematically utilized to provide complete intelligent answers to a wider range of queries. We consider two commonly used classes of semantic constraints called implication and referential constraints, and show that the completeness of intelligent answers with respect to semantic constraints can be reduced to the semantics-based query containment problem