A LOGIC-BASED APPROACH TO QUERY-PROCESSING IN FEDERATED DATABASES

Extant work on federated databases has concentrated either on schema i ntegration using semantic models or on query processing using the rela tional/extended relational model, but both issues have not been addres sed using a single framework. In this paper, we explore an alternative approach to database integration using Horn-clause logic as a canonic al, intermediate representation. First-order logic is used as a langua ge for expressing the integration of component schemas into a global s chema, as well as for specifying integrity constraints associated with global and component schemas. A language based on first-order logic p rovides the required expressiveness for canonical representation of th e global schema at the intermediate level. Global to local query mappi ng is achieved through the procedural interpretation of logic programm ing. Query optimization is performed through transformations using int egrity constraints, such as functional, inclusion, and data integratio n dependencies. PROLOG has been used for implementing some of the algo rithms described in this paper. The logic-based approach provides a un iform approach for supporting an integrated view of a set of heterogen eous databases, as well as its implementation.