The Omg Notification Service Study

In recent years, the development of distributed computing technique was much rapider then ever. This vigorous technique depending on computer networks has been applied a lot to a variety of applications. CORBA specification, which is developed and maintained by Object Management Group (OMG), provides the platform-independent program interface and models for those distributed computing applications that are potable and Object-Oriented. In the specification, Object Management Architecture (OMA) defined a series of services, which provide the higher system level services above the basic ORB functionalities. These services deal with kernel level functionalities, and all of them constitute the framework of advanced tools and operational functionalities.Commonly, CORBA uses synchronous communication mechanism. A client who had got the reference of the destination object and then sent out the request would block itself, till the result was sent back. However, as to most distributed applications, this blocking mechanism is not applicable because the restriction of the close coupling status of both sides in the communication makes it impossible to divide the message suppliers from those who are interested to the message. The specification of Notification Service established by OMG provides a pretty good solution to the problem mentioned above. The Notification Service provided a decoupled asynchronous communication mechanism to the users of distributed systems. The task of this article is to deeply research the impletmentation technique, basing on the definition of the Notification Service, then to design and implement a new Notification Service system that satisfies the requirement of Real-Time systems.What we had analyzed is ORBacus Notify, by IONA inc. This typical system maked full use of the mechanisms in CORBA2.3, such as POA, multithread, etc. And we had done such jobs with another Notification Service system that based on TAO, a different distributed middleware. After that, we had compared its ideas with those in ORBacus Notify. In this article, we will discuss the events communication, Filtering and Shared Subscription of ORBacus Notify in detail. Also we will introduce the implementation ideas of TAO Notification Service briefly. Then do some analyses on the performance gap due to the different implementation ideas of two systems.In a distributed environment, the transportation of events should be Real-time in many systems and applications. This means the events must be transported in PRI. Traditional Notification Service systems are deficient to achieve this. To solve this, we had designed and implemented a new Notification Service system. According to the requirements of users in different grains, we implemented the events transporting with PRI in two different layers. In the implementation, we used Real-Time CORBA and gave an efficient sorting algorithm In this article, we will introduce the background of the Real-Time Notification Service, the objective of our design and the concrete implementation on the two layers, in detail. At the end of the article, we will make analysis to our Notification Service system, and present a typical application scenario.