Answering queries using materialized views with disjunctions

We consider the problem of answering datalog queries using materialized views. More specifically, queries are rewritten to refer to views instead of the base relations over which the queries were originally written. Much work has been done on program rewriting that produces an equivalent query. In the context of information integration, though, the importance of using views to infer as many answers as possible has been pointed out. Formally, the problem is: Given a datalog program P is there a datalog program P-v which uses only views as EDB predicates and (i) produces a subset of the answers that P produces and (ii) any other program P-v' over the views with property (i) is contained in P-v? In this paper we investigate the problem in the case of disjunctive view definitions.