APPLICATION-SPECIFIC TRANSACTION MANAGEMENT IN MULTIDATABASE SYSTEMS

We present a transaction model for multidatabase systems with autonomo us component systems, coined heterogeneous 3-level transactions. It ha s become evident that in such a system the requirements of guaranteein g full ACID properties and full local autonomy can not be reconciled. In the heterogeneous 3-level transaction model, semantics of actions a nd specific properties of the architecture of multidatabase systems an d of applications are utilized to define application specific compromi ses between these competing goals. We consider different definitions o f conflicts between actions together with application specific sets of allowed (autonomous) local transactions and global subtransactions. A formal model for serializability is given. It is proven that heteroge neous 3-level transactions guarantee all consistency constraints that are ensured in serial executions. In contrast to most other models, we do not require data to be partitioned into global and local data. In particular, heterogeneous 3-level transactions even allow the same dat a to be updated by local and global transactions in parallel, if these updates are found to be semantically non-conflicting. Recovery is han dled by inverse actions. We present a formal framework for this approa ch which is fully integrated into serializability theory by considerin g inverse actions as ordinary actions. This has an important impact on the relationship of concurrency control and recovery in our model: By changing the definition of conflicts between actions in order to tail or the model according to application needs, recovery is implicitly af fected and no further explicit adaptation of recovery algorithms is ne cessary. The heterogeneous 3-level transaction model assumes component database systems to support ACID transaction properties. Further prop erties of local transactions or interfaces of the component database s ystems are not required. We describe a prototype implementation of het erogeneous 3-level transactions in the object-oriented database system VODAK.