Advanced transaction management for supporting interoperability in multidatabase systems
Abstract
This thesis examines approaches to the preservation of multidatabase consistency through concurrency control and atomic commitment. Local extensibility is proposed as the general principle to govern the execution of global transactions. Under this principle, we define those properties which will permit the execution of global transactions to interleave with the globally uncontrolled execution of local transactions while maintaining multidatabase consistency. Our discussion depends only upon the basic assumptions of the serializability and recoverability of local database systems. The thesis first develops a theoretical basis for concurrency control which preserves the isolation of local and global transactions. Using the conflicting and sharing properties of global transactions, three correctness criteria are proposed and their limitations are discussed. We then propose an approach to ensuring the correctness of non-serializable global and local transaction executions. In this approach, transaction views of a database are related to integrity constraints. A correctness criterion termed view-based two-level serializability is proposed to relax global serializability. The practical issues of the enforcement of these criteria on the execution of global transactions are also addressed. The thesis then develops a new approach to atomic commitment by ensuring a weaker form of the atomicity (called semi-atomicity) of flexible transactions. We offer a fundamental characterization of the flexible transaction model and precisely define the concept of semi-atomicity. We investigate the commit dependencies among the subtransactions of a flexible transaction. These dependencies are used to control the commitment order of the subtransactions. We next identify those restrictions that must be placed upon a flexible transaction to ensure the maintenance of its semi-atomicity. A global transaction management scheme for preserving the semi-atomicity and isolation of global transactions is then developed. Finally, the thesis investigates the possibility of decomposing global transactions to permit each global transaction to have more than one global subtransaction at a local site. A theory upon which we ground the decomposition of global transactions in multidatabase systems is advanced. This theory includes a sufficient condition for the decomposition of global transactions to preserve the consistency property of global transactions. A new correctness criterion for concurrency control is also proposed.
Degree
Ph.D.
Advisors
Bhargava, Purdue University.
Subject Area
Computer science
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