Integration of Different Commit/Isolation Protocols in CSCW Systems with Shared Data

• Authors: Lars Frank
• Venue: PSI '99 Proceedings of the Third International Andrei Ershov Memorial Conference on Perspectives of System Informatics
• Year: 1999

Traditional database systems use ACID properties (Atomicity, Consistency, Isolation and Durability) to implement recovery and concurrency control. However, this implementation is not always appropriate in distributed real time systems and in systems with long-lived transactions. For example, long-lived transactions may be active for days, and at the same time other transactions may need access to data, locked by the long-lived transactions. Therefore, extended transaction models have been developed. These transaction models only implement semantic ACID properties. That is, from an application point of view the system should function as if the traditional ACID properties were implemented. Multi user word processing, CAD and CASE systems may both be distributed and have long-lived transactions. Therefore, extended transaction models may be useful in Computer Supported Cooperative Work (CSCW), where users work with shared data. In this paper we will try to integrate the research in extended transaction models with the CSCW research, which for many years have been aware of the shortcomings of the traditional ACID properties. In the transaction model in this paper the global atomicity property is implemented by combining the possibilities of either forcing the remaining updatings of a transaction to be executed or compensating the already executed updatings of the transaction. The global consistency property may be managed by the CSCW system and/or by human beings supported by tools. The global isolation property is implemented by using countermeasures to the missing isolation of the updating transactions. The global durability property is implemented by using the durability property of the local CSCW/DBMS systems. In the extended transaction model described above we will incorporate some of the most promising CSCW commit/isolation features known from the scientific CSCW literature.