Research On Event Model Technology In The Rules Of ECA

The active database manage system is one of the main research areas of database technologies. It is the outcome that the active technique and the database techniques combine together, the active mechanisms of the active database management system are carried out by the way that some rules imbed the database system in advance.The system supplies an automatic monitoring model, and it checks if all sorts of events included in the rules. Once it notices some certain event happens, it will react upon this. The model is defined as the event monitoring of active database. The event model the thesis illustrates is defined and designed on the basis of the monitoring. Through the monitoring, DBMS can actively perform some actions designed by the users. Function such as the complete restraint, the access control, exception processing, the surveillance and the warning, the condition switch automatic cut over, the retrieval strategy cut, and even complex function and so on deductive inference and real-time processing can realize by one kind of unified mechanism. Therefore, the event is the source of active database. The change of the inner and outside database triggers the occurrence of events. The corresponding condition is appraised only when the event monitored is occurred , if the condition holds, then it carries out the action which is defined in advance. With the development of the active database, the Event Condition Action (ECA) rule theory is set up. So the event in the rule of ECA is the key point to this. In recent years, researches on active database event model were popular, and focused on the expression and monitoring technology. Through consulting a lot of literature in our country and abroad concerning active database system, these systems have some major shortcomings:1. The meanings of the event model are not plentiful, and cannot express some more complicated meanings.2. The indicating methods of the trigger event are very limited, and cannot provide the users an indicating method that they can freely construct and design.3. Event cannot be repeatedly used for many times.4. The inner storage and expressing form of event are too complicated, and to be optimized further.5. The monitoring methods of complex events are inefficient.The thesis improves the five shortcomings mentioned above, and enriches the meaning expression of event model. Thus the users can freely construct and design the events they need. Adopting event tree structure, complex event expression is stored. One method of new compound event monitors is proposed , it is very efficient than the traditional method.The occurrence of events finally shows on a certain time point or time span, so the occurrence of complex events may be related to a group of time point or time span. Therefore, the time of the event becomes the core of event. The researches on this are deeply conducted. That is to say, the occurrence of event is related not only to the time, but also to the historical situation to some complex events, and what to occur can also be predicated. All these questions can be summarized to the tense of event, and it will be discussed in detail in Chapter Three and further expands the definition of character regarding event, which is not based on time point but time span. Thus, the expressing form of complex event is to be optimized further.The way carried out of the active database is some active functions integration in the database system, that is to say , some ECA rules imbed the database system. If we are to carry out the question of the ECA rule imbedding, we are first to solve the question of the event imbedding. The event imbedding first needs to solve the question of event knowledge model in the event model technology. the paper introduces the OOD(Orient Object Design) thought, according to the event origin,definition,classification and operation, it gives the class definition and the OOD(Orient Object Design) express of the abstract event, strengthens the expression ability of the event model, enrichs the construction of the traditional event knowledge model, thus it lay on the certain foundation for the realization of the seamless embedding of for event. The data,the event,the condition and the rule and so on carry on definition and the transfer by the class form, all kinds of active demands in the active database management system are designed and carried out, then carried out all kinds of complex intention for the user.Concerning event monitoring, the thesis summarized the four event monitoring methods to active database widely used in recent years: time graphs method, event graphs method, Petri net method and auto-machine method. After fully analyzing the four methods, a new event monitoring method was presented: the Event-time Graphs method. This method combines the time graphs and event graphs methods together, it clears structure of complex event, effectively expresses the occurrence of the event example participated in all history events,marks the initial and the termination of complex event , solves the question of the event parameter transmission, in the different situation nimbly utilizing four kind of consumptions patterns effective enhances monitor efficiency and saves the storage space. The thesis also provides the calculating method under the recent and continuous surroundings. In brief, completing the event monitor combination these two methods has some many merits, but also has some shortcomings, that is, when the expression form of event is extremely complicated, the event tree structure constituted event chart will extremely be complicated too, but the event tree often will carry on the dynamic foundation in the process of system operation, thus, system can pay for very high price when analyzing the form expression of event and constructing the tree structure. Finally, according to the basic principle of the knowledge model of structure and the monitor method of event model in the active database, on the base of theory viewpoint found designs the important component part of active database management system: The event monitoring, and carries out outline design of the event monitoring by the OOD (Orient Object Design) method.