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Event-driven architecture (EDA) is a software architecture pattern promoting the production, detection, consumption of, and reaction to events. An ''event'' can be defined as "a significant change in state".〔K. Mani Chandy Event-Driven Applications: Costs, Benefits and Design Approaches, ''California Institute of Technology'', 2006〕 For example, when a consumer purchases a car, the car's state changes from "for sale" to "sold". A car dealer's system architecture may treat this state change as an event whose occurrence can be made known to other applications within the architecture. From a formal perspective, what is produced, published, propagated, detected or consumed is a (typically asynchronous) message called the event notification, and not the event itself, which is the state change that triggered the message emission. Events do not travel, they just occur. However, the term ''event'' is often used metonymically to denote the notification message itself, which may lead to some confusion. This architectural pattern may be applied by the design and implementation of applications and systems which transmit events among loosely coupled software components and services. An event-driven system typically consists of event emitters (or agents), event consumers (or sinks), and event channels. Emitters have the responsibility to detect, gather, and transfer events. An Event Emitter does not know the consumers of the event, it does not even know if a consumer exists, and in case it exists, it does not know how the event is used or further processed. Sinks have the responsibility of applying a reaction as soon as an event is presented. The reaction might or might not be completely provided by the sink itself. For instance, the sink might just have the responsibility to filter, transform and forward the event to another component or it might provide a self-contained reaction to such event. Event channels are conduits in which events are transmitted from event emitters to event consumers. The knowledge of the correct distribution of events is exclusively present within the event channel. The physical implementation of event channels can be based on traditional components such as message-oriented middleware or point-to-point communication which might require a more appropriate . Building applications and systems around an event-driven architecture allows these applications and systems to be constructed in a manner that facilitates more responsiveness, because event-driven systems are, by design, more normalized to unpredictable and asynchronous environments.〔Jeff Hanson, (Event-driven services in SOA ),''Javaworld'', January 31, 2005〕 Event-driven architecture can complement service-oriented architecture (SOA) because services can be activated by triggers fired on incoming events.〔〔Carol Sliwa (Event-driven architecture poised for wide adoption ), ''Computerworld'', May 12, 2003〕 This paradigm is particularly useful whenever the sink does not provide any . SOA 2.0 evolves the implications SOA and EDA architectures provide to a richer, more robust level by leveraging previously unknown causal relationships to form a new event pattern. This new business intelligence pattern triggers further autonomous human or automated processing that adds exponential value to the enterprise by injecting value-added information into the recognized pattern which could not have been achieved previously. Computing machinery and sensing devices (like sensors, actuators, controllers) can detect state changes of objects or conditions and create events which can then be processed by a service or system. Event triggers are conditions that result in the creation of an event . ==Event structure== An event can be made of two parts, the event header and the event body. The event header might include information such as event name, time stamp for the event, and type of event. The event body provides the details of the state change detected. An event body should not be confused with the pattern or the logic that may be applied in reaction to the occurrence of the event itself. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Event-driven architecture」の詳細全文を読む スポンサード リンク
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