ACTA: The SAGA Continues

ACTA is a comprehensive transaction framework that permits a transaction modeler to specify the e ects of extended transactions on each other and on objects in the database. ACTA allows the speci cation of (1) the interactions between transactions in terms of relationships between signi cant (transaction management) events, such as begin, commit, abort, delegate, split, and join, pertaining to di erent transactions and (2) transactions' e ects on objects' state and concurrency status (i.e., synchronization state). Various extended traditional models have been proposed to deal with applications that involve reactive (endless), open-ended (long-lived) and collaborative (interactive) activities. One such model is Sagas [GS87] A Saga is a set of relatively independent (component) transactions T 1 , T 2 ,..., T n which can interleave in any way with component transactions of other Sagas. Components can commit even before the Saga commits. However, if the Saga subsequently aborts, e ects of the committed components are nulli ed through the invocation of compensating transactions. After giving a brief introduction to the modeling primitives of ACTA, we illustrate their use by giving a complete formal characterization of Sagas. Subsequently, the reasoning power of ACTA is shown by proving properties of Sagas. Finally, the exibility of ACTA is displayed through a series of variations to the original model of Sagas, each variation coming out of changes to the formal characterization of Sagas. This is a reprint of Chapter 10 of \Transactions Models for Advanced Database Applications," edited by A. K. Elmagarmid of Purdue University and published by Morgan Kaufmann (1992) This material is based upon work supported by the N.S.F. under grant CDA-8922572. E-mail: [email protected], [email protected]. Panos K. Chrysanthis Krithi Ramamritham