Concurrent transaction execution in multidatabase systems

Multidatabase serializability is defined as an extension of the well-known serializability theory in order to provide a theoretical framework for research in concurrency control of transactions over multidatabase systems. Also introduced are multidatabase serializability graphs which capture the ordering characteristics of global as well as local transactions. Two schedulers that produce multidatabase serializable histories are described. The first scheduler is a conservative one which only permits one global subtransaction to proceed if all of the global subtransactions can proceed for any given global transaction. The `all or nothing´ approach of this algorithm is simple, elegant, and correct. The second scheduler is more aggressive in that it attempts to schedule as many global subtransactions as possible as soon as possible. A distinguishing feature of this work is the environment that it considers; the most pessimistic scenario is assumed, where individual database management systems are totally autonomous with no knowledge of each other. This restricts the communication between them to be via the multidatabase layer and requires that the global scheduler `hand down´ the order of execution of global transactions