Context Based Semantics for Federated Databases

In this paper we describe an application of contexts to distributed database modeling. In many applications which use a large amount of information, knowledge is partitioned and represented in a set of databases (DB) integrated in a federated database (FDB). A FDB is a collection of distributed, partial, redundant and partially autonomous DBs. Distribution, redundancy, partiality, and autonomy generate many problems such as semantic heterogeneity, update propagation, inter-schema dependencies, and query distribution. A formal treatment of these problems is necessary to define FDB management systems with correct behaviour. Several approaches have been proposed in the past. However, they al fail to represent all these issues in an uniform way. This failure, from our perspective, is due to the fact that these approaches do not explicitly treat distribution, redundancy, partiality, and autonomy. In this paper we develop a context based semantics, called local models semantics, for FDB. Local model semantics associates to each DB of the federation a context, formalized as a set of models for the single DB. in this paper we show how a context based semantics allows for an explicit representation of distribution, redundancy, partiality, and autonomy. We show how semantics of contexts is adeguate for the formalization of the logical schema of a federated database by providing the local model semantics for a motivating example