Query folding

Query folding refers to the activity of determining if and how a query can be answered using a given set of resources, which might be materialized views, cached results of previous queries, or queries answerable by other databases. We investigate query folding in the context where queries and resources are conjunctive queries. We develop an exponential time algorithm that finds all complete or partial foldings, and a polynomial time algorithm for the subclass of acyclic conjunctive queries. Our results can be applied to query optimization in centralized databases, to query processing in distributed databases, and to query answering in federated databases.