Design Of Active Mechanism In Mobile Database Systems

In a mobile computing environment, mobile host is characterized by mobility and variety of connected condition with wireless network. Those characteristics require the mobile database system which serves mobile hosts responds to them accordingly. In active database systems, establish relevant rules in advance, using events as trigger to manipulate database, can provide active function for mobile database.In order to use active mechanism in mobile database systems, modification of traditional active rules systems is needed. In mobile computing environment, its difference is not only on events, but also on architecture , events detect mode and technology , condition evaluation triggering and execution of rules.This paper discusses how to introduce active mechanism into mobile database systems. First, Based on the ECA (event condition action) rule system model of active database adopted in this paper, diversified mobile events are defined, and a temporal logic description for events is given. The new event content supports the event triggering of active database system, thereafter supports active process of a mobile database system efficiently. Second, discuss events detection in mobile database systems. Mobile database system is the extension of a distributed database system. Besides characters such as distributed, concurrent, asynchronous and stochastic in distributed database system, events in a mobile database system are characterized by delay and disorder for instability of wireless network. In order to detect them, a Petri Net event detection model CCPN is proposed in this paper. Using the model, asynchronous and concurrent events in a mobile database system are modeled frankly and flexibly, temporal events detection is supported also. Meanwhile, related technologies about detecting events in disconnected or mobile condition are discussed. Third, the method of ECA rules embed in mobile database systems-the architecture of based on ECA mediator is discussed. Fourth, discuss composite condition evaluation which based on mobile condition and database conditional transition and it's optimize method. Finally, execution semanteme of rules and execution mode of mobile transaction and their compare is given.