Data exchange: Query answering for positive query with at most one inequality

In a data exchange system the correctness of the system depends on data exchange semantics. This can be well verified by using query answering. In the close world assumption (CWA) two types of answers are obtained, one is certain answer, which ignores the null values, another is maybe answer, which considers the null values. In this thesis, we give a procedure for computing a finite representation of the maybe answer. Here we use positive conjunctive queries with at most one inequality. Finally, the queries are tested on some practical data exchange sceneries and the results are compiled.