DORMIA: a distributed system for mobile information access

A new distributed information system called DORMIA has been developed to support mobile information access from portable computers with weak network connectivity. This paper describes the design and implementation of DORMIA. The design aims to provide high availability, heterogeneous support and high efficiency. To maximize availability, users can read or write any accessible replica. A scalable algorithm based on logical clocks has been developed to keep object replicas consistent. Novel methods are used to detect and resolve conflicts based on record level checking. The use of reliable multicast provides effective means to update the replicas. The use of CORBA IDL and Java to define interfaces provides the full heterogeneous support. To enable a mobile client to continue accessing critical data during temporary disconnection, we have developed the pre-fetching and reintegration mechanism to support the disconnected operation. A performance measurement study is subsequently conducted with the prototype implementation. The results indicate that the system developed is highly efficient