Semantic serializability: A correctness criterion for processing transactions in advanced database applications

摘要

Serializability requires that the execution of each transaction must give the illusion to be an atomic action, i.e., the execution of a set of transactions must appear to be a serial one. This requirement, however, is too strong and unnecessarily restricts concurrency among transactions, when semantic information is available for the transaction processing mechanism. In this paper, a new correctness criterion for concurrent execution of database transactions, denoted semantic serializability, is proposed. Semantic serializability is based on the use of semantic information about database objects (and not about transactions). The main idea of our proposal is to provide different atomicity views for each transaction and, for this reason, to allow interleavings among transactions which are nonserializable, but which preserve database consistency. We develop two concurrency control protocols, which are based on semantic serializability. One protocol is based on a locking-mechanism and the other one uses a non-locking approach. Our proposal is suitable to a wide variety of advanced database applications, such as CAx, MDBS, GIS and WFMS.