ON RELAXING SERIALIZABILITY BY CONSTRAINING TRANSACTION READSETS

Although, concurrency control in database systems is primarily based o n serializability, many recent applications have rendered traditional serializability-based criteria inefficient or inappropriate. However, non-serializable executions may violate database consistency. In this paper, we propose a new approach to ensuring the correctness of non-se rializable executions. The approach is based on relating transaction v iews of the database to the integrity constraints of the system. The u nderlying concepts of view closure and view consistency are defined. T hen, drawing upon this approach, we develop a new correctness criterio n for multidatabases, which are confederations of pre-existing heterog eneous and autonomous distributed database systems. This criterion, ca lled view-based two-level serializability, relaxes serializability whi le respecting the autonomy of local database systems and preserving mu ltidatabase consistency. We investigate the application of the criteri on to various practical multidatabase scenarios and discuss implementa tion issues. (C) 1997 Elsevier Science Ltd. All rights reserved.