Discovering and using entity mappings in federated databases

In the context of a federated database containing similar information in local component databases, we consider the problem of discovering the different local representations which database designers might use to map the same entity. An extension of the normal SQL system catalog to hold additional domain metadata is discussed. This enables common local mappings to be discovered and allows SQL retrieval queries expressed in terms of the logical federated schema to be transformed to match the appropriate local database schema. The result is a practical means of coping with differing mappings in federated databases without having to resort to special higher order languages or a layer of information mediation middleware.