On relaxing serializability by constraining transaction readsets

Although, concurrency control in database systems is primarily based on 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-serializable executions. The approach is based on relating transaction views of the database to the integrity constraints of the system. The underlying concepts of view closure and view consistency are defined. Then, drawing upon this approach, we develop a new correctness criterion for multidatabases, which are confederations of pre-existing heterogeneous and autonomous distributed database systems. This criterion, called view-based two-level serializability, relaxes serializability while respecting the autonomy of local database systems and preserving multidatabase consistency. We investigate the application of the criterion to various practical multidatabase scenarios and discuss implementation issues.