A logic-based approach to query processing in federated databases

Abstract

Extant work on federated databases has concentrated either on schema integration using semantic models or on query processing using the relational/extended relational model, but both issues have not been addressed using a single framework. In this paper, we explore an alternative approach to database integration using Horn-clause logic as a canonical, intermediate representation. First-order logic is used as a language for expressing the integration of component schemas into a global schema, as well as for specifying integrity constraints associated with global and component schemas. A language based on first-order logic provides the required expressiveness for canonical representation of the global schema at the intermediate level. Global to local query mapping is achieved through the procedural interpretation of logic programming. Query optimization is performed through transformations using integrity constraints, such as functional, inclusion, and data integration dependencies. PROLOG has been used for implementing some of the algorithms described in this paper. The logic-based approach provides a uniform approach for supporting an integrated view of a set of heterogeneous databases, as well as its implementation.