Advances in wireless communications technology make it possible to realize a data processing paradigm that eliminates geographical constraints from data processing activities. Multidatabase can be viewed as a database system formed by independent databases joined together with a goal of providing uniform access to the local database management systems (DBMS). The mobile data access system (MDAS) is a multi-database system (MDBS) that is capable of accessing a large amount of data over a wireless medium. It is necessary that the MDAS provide timely and reliable access to shared data. The transaction technique presented in Pitoura and Bhargava  is based on an agent-based distributed computing model. Agents may be submitted from various sites including mobile stations. There are several multidatabase concurrency control schemes such as site-graph locking  and V-Lock.  None of the reviewed techniques handle mobile transactions and long-lived transactions in a multilayered approach, and hence global transactions are not executed as consistent units of computing.
In this chapter, we propose a WAP-enabled transaction model for the MDAS that addresses the deficiencies that exist in the current literature. The model is built on the concept of global transactions in multidatabases. In Bright and coworkers,  the model uses a hierarchical structure that provides an incrementally concise view of the data in the form of schemas. The hierarchical data structure of the Summary Schemas Model (SSM) consists of leaf nodes and summary schema nodes. Accessing a lower-most node takes time in the hierarchical structure. However, these systems have not been designed to cope with the effects of mobility. The goal of this chapter is to present a WAP-enabled transaction model for the MDAS that handles mobile transactions and long-lived transactions in a multilayered approach.
Section 20.2 gives the background material on Wireless Application Protocol (WAP), mobile computing environment, and mobile database systems. Various mobility applications are discussed in Section 20.3. The WAP-enabled transaction model is introduced in Section 20.4. An implemented sample application of the proposed model is given in Section 20.5. Simulation results of the proposed model are presented in Section 20.6. Conclusions are given in Section 20.7.
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