Consistency in Intermittently Connected Distributed Systems

Mobile computing introduces a new form of distributed computation in which communication is most often intermittent, low-bandwidth, or expensive, thus providing only weak connectivity. We have developed a replication schema tailored for such environments, that seeks to adapt consistency guarantees to networking conditions. Bounded inconsistency is defined by allowing controlled deviation among copies located at weakly connected sites. The database interface is extended with weak operations that permit access to local, potentially inconsistent copies and make conditional updates. The usual operations, called strict in this framework, are also supported and offer access to consistent data and perform permanent updates. The proposed model provides for disconnected operation, since mobile clients can operate even when disconnected by using weak operations. A balanced use of weak and strict transactions can efficiently reduce network usage and latency. Adjusting the degree of divergence among copies provides additional support for adaptability. We have evaluated the performance of the schema for a range of networking conditions and varying percentages of weak transactions by using an analytical model developed for this purpose.

Recent Publication and Reports

Data Consistency in Intermittently Connected Distributed Systems,: with B. Bhargava. In IEEE Transaction on Knowledge and Data Engineering , 11(6), pp 896-915, Nov/Dec 1999.
A Replication Schema to Support Weak Connectivity in Mobile Information Systems: In Proceedings of the 7th International Conference on Database and Expert Systems Applications (DEXA) , September 1996.; An extended version appears as: University of Ioannina, Computer Science Department, Techical Report No: 96-08; Slides of the presentation at the DEXA Conference, September 1996.
Maintaining Consistency of Data in Mobile Distributed Environments: with B. Bhargava. In Proceedings of the 15th International Conference on Distributed Computing Systems, pp. 404--413, May 1995.; Slides of the presentation at the DCS Conference, May 1995.
A Framework for Providing Conistent and Recoverable Agent-Based Access to Heterogeneous Mobile Databases: with B. Bhargava. Sigmod Record , pp. 44--49, September 1995.; Also available as Technical Report CSD 95--011, Computer Science, Purdue University, February 1995.
Revising Transaction Concepts for Mobile Computing: with B. Bhargava. In Proceedings of the 1st IEEE Workshop on Mobile Computing Systems and Applications , pp. 164--168, Dec 1994. An one--page abstract also appears in TCOS Bulletin, Spring 1995.
Building Information Systems for Mobile Environments: with B. Bhargava. In Proceedings of the 3rd International Conference on Information and Knowledge Management, pp. 371--378, Nov 94.