Integrating heterogeneous OO schemas

To eliminate semantic conflicts among the heterogeneous databases involved in a cooperation, a set of correspondence assertions for declaring their semantic relationships have to be constructed by DBAs or by users. Normally, four set relationships between object classes: equivalence, inclusion, intersection, and exclusion will be defined to provide knowledge about correspondences that exist among the local schemas. In this paper, we would like to introduce a new assertion, the so-called derivation assertion, to accommodate more heterogeneities, which can not be treated by the existing methodologies. As an example, consider two local object-oriented schemas: S₁ and S₂ and assume that S₁ contains two classes: parent and brother, and S₂ contains a class: uncle. A derivation assertion of the form: S_l(parent, brother)→S₂(uncle) can specify their corresponding semantic relationship clearly, which can not be established otherwise. We claim that this kind of assertions is necessary for the following reason. Imagine a query concerning uncle, submitted to the integrated schema from S₁ and S₂. If the above assertion is not specified, the query evaluation will not take schema S₁ into account and thus the answers to the query can not be correctly computed in the sense of cooperations