As technological advances are made in software and hardware, the feasibility of accessing information "any time, anywhere" is becoming a reality. Furthermore, the diversity and amount of information available to a given user is increasing at a rapid rate. In a mobile computing environment, a potentially large number of users may simultaneously access the global data; therefore, there is a need to provide a means to allow concurrent management of transactions. Current multidatabase concurrency control schemes do not address the limited bandwidth and frequent disconnection associated with wireless networks. This paper proposes a new hierarchical concurrency control algorithm. The proposed concurrency control algorithm, v-lock, uses global locking tables created with semantic information contained within the hierarchy. The locking tables are used to serialize global transactions, detect and remove global deadlocks. Additionally, data replication, at the mobile unit, is used to limit the effects of the restrictions imposed by a mobile environment. The replicated data provides additional availability in case of a weak connection or disconnection. Current research has concentrated on page and file-based caching or replication schemes to address the availability and consistency issues in a mobile environment. In a mobile, multidatabase environment, local autonomy restrictions prevent the use of a page or file-based data replication scheme. This paper proposes a new data replication scheme to address the limited bandwidth and local autonomy restrictions. Queries and the associated data are cached at the mobile unit as a complete object. Consistency is maintained by using a parity-based invalidation scheme. A simple prefetching scheme is used in conjunction with caching to further improve the effectiveness of the proposed scheme. Finally, a simulator was developed to evaluate the performance of the proposed algorithms. The simulation results are presented and discussed.

As technological advances are made in software and hardware, the feasibility of accessing information "anytime, anywhere" is becoming a reality. There are similarities involved in accessing information in a multidatabase environment and a mobile computing environment. We have discussed the characteristics of a wireless-mobile computing environment superimposed on a multidatabase system to realize a system capable of effectively accessing a large amount of data over a wireless medium. In order to limit the effects of the restrictions imposed by a mobile environment, data duplication is used at the mobile unit. The duplicated data at the mobile node provide additional availability in case of a weak connection or disconnection. In such an environment, it is important to retain the consistency between the data residing on fixed nodes and mobile nodes. Current research has concentrated on page- and file-based caching or replication schemes to address the availability and consistency issues in a mobile environment. In a mobile multidatabase environment, local autonomy restrictions prevent the use of a page- or file-based data duplication scheme. We propose a new data duplication scheme to address the limited bandwidth and local autonomy restrictions in such an environment. Queries and their associated data are cached at the mobile unit as a complete object. Consistency is maintained by using a parity-based invalidation scheme. Additionally, a simple prefetching scheme is used in conjunction with caching to further improve effectiveness of the proposed scheme.