Multiplex: A Formal Model for Multidatabases and Its Implementation

The integration of information from multiple databases has been an enduring subject of research for almost 20 years, and many di erent solutions have been attempted or proposed. Missing from this research has been a uniform framework. Usually, each solution develops its own ad-hoc framework, designed to address the particular aspects of the problem that are being attacked and the particular methodology that is being used. To address this situation, in this paper we de ne a formal model for multidatabases, which we call Multiplex. Multiplex is a simple extension of the relational model, which may serve as a uniform abstraction for many previous ad-hoc solutions. Multiplex is based on formal assumptions of integrability, which distinguish between scheme and instance reconcilability among independent databases. Multiplex supports database heterogeneity, and it provides several degrees of freedom that allow it to model actual situations encountered in multidatabase applications. In addition, in situations in which a single answer is not obtainable (either because the global query is not answerable, or there are multiple candidate answers), Multiplex de nes approximative answers. Finally, Multiplex provides a practical platform for implementation. A prototype of such an implementation is described brie y. This work was supported in part by ARPA grant, administered by the O ce of Naval Research under Grants No. N0014-92-J-4038 and N0060-96-D-3202.