Research And Implementation Of The Active Rules In Active Database System DM3-ADB

Traditional DBMS is operated only under the explicit instructions. But Active DBMS can automatically monitor the state of database system, and the system will trigger the predefined operation as soon as a sensitive state appears. Compared with Traditional DBMS, Active DBMS has great advantage. So there must have great practical signification to add active rule to DM3 which is a distributed relational database management system and extend DM3 into DM3-ADB which is an active DBMS.? DM3-ADB is composed of active rule management module and active rule execution module. The active rule management module can be divided into rule definition, deletion, modification and storage. In rule definition, DM3-ADB adds temporal event, supports compound event operators, and uses DM_SQL block to define rule action, which enhances rule expression capacity greatly. For storing rule flexibly and high efficiency, in rule storage DM3-ADB uses a three-level storage model of active rule: table label, rule catalogue, rule body.The active rule execution module can be divided events detection, condition evaluation, rule scheduling and rule execution. The core of DM3-ADB rule execution module is to construct a virtual machine. When a rule is triggered, DM3-ADB extracts virtual machine instructions of rule action and executes these instructions by virtual machine.How to judge the termination and confluence of behavior of set of rules is the key point of active database. Based on analysis of some pertinent method, DM3-ADB limits the maximal rule triggered level to assure rule termination, and adopts priority to analyze rule confluence.