Resumen
A common characteristic of today's information systems is the distribution of data among a number of autonomous and heterogeneous repositories as of September 1998. Increasingly, these repositories are database management systems, but there is still a very large volume of data that is stored in file systems, spreadsheets and other forms. A fundamental challenge in next-generation information systems is to provide interoperability autonomous and potentially heterogeneous repositories. The commercial state-of-the-art practice in addressing the interoperability of database management system (DBMS) is to build gateways. This approach is quite restricted and provides only a partial solution. None of these systems properly deal with semantic or structural heterogeneity of the stored data. An alternative approach to achieving interoperability among DBMSs is the multidatabase approach. A multidatabase system resides unobtrusively on top of existing database systems and presents a single database illusion to its users. In particular, a multidatabase system maintains a single global database schema against which its users issue queries and updates.