Concurrency Control in Groupware Systems

Abstract. Groupware systems are computer-based systems that support two or more users engaged in a common task, and that provide an interface to a shared environment. These systems frequently require fine-granularity sharing of data and fast response times. This paper distinguishes real-time groupware systems from other multi-user systems and dis-cusses their concurrency control requirements. An algorithm for concurrency control in real-time groupware systems is then presented. The advantages of this algorithm are its sim-plicity of use and its responsiveness: users can operate di-rectly on the data without obtaining locks. The algorithm must know some semantics of the operations. However the algorithm’s overall structure is independent of the semantic information, allowing the algorithm to be adapted to many situations. An example application of the algorithm to group text editing is given, along with a sketch of its proof of cor-rectness in this particular case. We note that the behavior desired in many of these systems is non-serializable. 1