Abstract
Answering queries using views amounts to computing the answer to a query having information only on the extension of a set of views. This problem is relevant in several fields, such as information integration, data warehousing, query optimization, etc. In this paper we address the problem of query answering using views for nonrecursive datalog queries embedded in a Description Logics (equipped with n-ary relations) knowledge base. We present the following results. Query answering using views is decidable in all cases. Specifically, if the set of all objects in the knowledge base coincides with the set of objects stored in the views (closed domain assumption), the problem is coNP complete, whereas if the knowledge base may contain additional objects (open domain assumption) it is solvable in double exponential time.