www.developer.com/design/article.php/3499031
By K. Mani Chandy and Jonathan Lurié Carmona and Robert Alexander April 20, 2005 In one type of system, the person who needs information is responsible for acquiring it: the patient is responsible for asking the doctor about drug interactions; the doctor is responsible for checking with the FDA, and the onus is on the FDA to find out facts about drugs from pharmaceuticals. In a different type of system, the organization that obtains information is responsible for propagating the information to organizations that need it (in other words, to subscribers) in a timely fashion: pharmaceuticals tell the FDA, which tells doctors, who tell patients. Thus, the time between the occurrence of a material event and the appropriate response is reduced.
EDA vs. SOA and Traditional Pub-Sub SystemsIn SOAs, the person who needs information is responsible for asking the person who has the information: The client invokes a service on a server, and the server has no responsibility other than to respond to service invocations. In EDA, the client who needs information is responsible for updating subscriptions (models, forecasts, and plans) at the server with the information, and the server is responsible for continuously propagating relevant information. Three aspects of EDA contracts make EDA more powerful than SOA:
Some might argue that EDA and the Event Web are nothing but well-known push technology. These skeptics miss the key point: Traditional push technologies and pub-sub systems exploit only a tiny fraction of the power of EDA for four reasons:
Traditional pub-sub systems exploit only a tiny fraction of the power of EDA because they use only simple subscriptions rather than sophisticated models. An example of a simple subscription is: "Send all messages dealing with 'Sales' to a subscriber." Designing good EDA systems requires creativity because of the many ways in which models can be distributed and shared between agents. Upcoming articles in this series will discuss designs of EDA systems. |
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