Using semantic correctness in multidatabases to achieve local autonomy, distribute coordination, and maintain global integrity

摘要

A multidatabase poses the following four, often contradictory, requirements. First, local databases require both design autonomy to accommodate the diverse legacy nature of the local databases, and execution autonomy to ensure that local transactions are not unduly blocked by global transactions. Second, management of global transactions must be distributed to avoid bottlenecks and to tolerate failure in the global database. Third, both local and global integrity constraints must be maintained. Finally, concurrent processing of transactions requires that execution histories be correct, an objective traditionally achieved with serializability. Although alternate forms of correctness have been proposed, none of the solutions advanced to date has simultaneously achieved all four requirements. We propose a transaction processing model that uses a semantics-based notion of correctness to achieve all four requirements simultaneously for applications that satisfy a certain set of properties. The support required for global transactions forms a separate layer at each site that respects both design autonomy and execution autonomy. Global transactions are managed at each site via a successor set mechanism so that site and communication failures do not impede transactions at operating sites. Semantic correctness encompasses three properties: ensuring that local and global integrity constraints are maintained, that transactions output consistent data and that all partially executed transactions can complete. A fourth property ensures that the successor set description is a valid refinement of the specification. These four properties must be proved for applications executed by our model. We show how model checking can automate, in part, the verification of the properties. (C) 2000 Elsevier Science Inc. All rights reserved. [References: 26]