A Active Federated Database Systems

Database management systems (DBMS) are becoming part of environments composed of large-scale distributed heterogeneous and networks of autonomous, loosely coupled components. In particular, federated database management systems (FDBMS) can be seen as networks that integrate a number of pre-existing autonomous DBMS which can be homogeneous or heterogeneous. They can use different underlying data models, data definition and manipulation facilities, transaction management, and concurrency control mechanisms. DBMS in the federation can be integrated by a mediator providing a unified view of data: a global schema, a global query language, a global catalogue, and a global transaction manager. The underlying transaction model considers, in general, a set of transactions synchronized by a global transaction. Synchronization is achieved using protocols such as the TwoPhase Commit protocol. FDBMS applications are built upon this global environment, and they interact with the mediator to execute global database operations (i.e., operations that can concern various DBMS in the federation). In order to illustrate intuitively the use of FDBMS, consider a financial context where a shareholder has two bank accounts in Mexico and in France managed by database applications. This person needs to execute banking operations either accessing the accounts independently or making applications cooperate to have a global view of his/her financial situation. Clearly, an FDBMS application would fulfill these requirements, letting to execute transparently banking global (e.g., consult of the global credit) and local operations (e.g., withdraw 1000 pesos from the account in Mexico). Assume now that shareholders need specific operations to be executed timely when certain conditions come up: