A model of concurrent, cooperating transactions in an object-oriented database

Abstract

We describe a model of transactions and concurrency control that supports cooperative task and data sharing among users. The model augments traditional correctness criteria, such as global consistency for individual transactions and serializability for concurrent transactions, with programmer-defined correctness criteria that uniformly integrate both data and application semantics. Individual transactions are not required to maintain global consistency. Rather, transactions cooperate in groups, such that transaction groups are the units of consistency. The context for the model is an extensible object-oriented database: abstract data types define the behavior and representation of their instance objects, and each object is accessed only by way of the strict operational interface defined by its type. Applications can incrementally contribute new types to the database. The model effectively represents a transaction management system that is programmable by knowledgeable application designers. Although developed toward the needs of applications that provide computer support for cooperative activities, such as office information systems, graphical programming environments, and CAD tools for electronic or mechanical domains, the model provides a framework for any application for which the traditional transaction model is too restrictive. The model's key features are a nested framework of transaction groups that encapsulate nonserializable data sharing and a method for localized specification of semantic correctness criteria for concurrent histories of cooperating transactions.