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An ESB also supports requirements such as security, orchestration, and transactionality. These exist in "hard-wired" integration methods, but are not available automatically in a service-oriented architecture. One of the key requirements for the ESB is to give loosely coupled, service-based integration methods a level of enterprise-class reliability and security.

A newer requirement for ESBs is the ability to allow not only loosely-coupled requests found in a service oriented architecture, but also to provide the infrastructure for an Event Driven Architecture (EDA). SOA and EDA provide complementary functionality. In EDA an event triggers a message to be sent to other applications that are decoupled from the application that triggered the event. This is an asynchronous operation as the recipient applications may receive or pick-up their messages at a later time, whereas the SOA messaging model is typically synchronous in nature.

What is Java Business Integration (JBI)?

JBI is an architecture for integration systems specifying plug-in components that interoperate by exchanging messages, rather than by interacting directly. This decoupling increases flexibility because each component needs to know how to interact with the JBI bus only and not with n number of other components. JBI components provide services, consume services, or sometimes both. There are two types of components: Service Engines (SE) and Binding Components (BC). The SEs provide business logic and transformation services. The BCs provide connectivity for applications that are external to the JBI. The separation of business and processing logic from communication logic makes the implementation of components much easierless complex.

The mediated message exchange between components is provided by the Normalized Message Router (NMR). The NMR routes normalized messages between service providers and consumers. A normalized message consists of two parts: the message content (payload) and the message metadata. The message metadata contains information such as security information, that can affect the processing of the message as it routes through the JBI. Messages flowing into the JBI, via binding components, are translated into a normalized (neutral) format, then routed to their destination. Prior to final delivery the normalized message is translated into the appropriate format for the recipient. A message can be routed through several JBI components depending on what processing is needed.

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There are many vendors that provide ESB solutions, but there is not universal agreeement agreement as to the best design or architecture for an ESB. LogicBlaze has implemented the ServiceMix ESB based on the JBI (JSR 208) specification in order to create a standards based ESB and the ServiceMix ESB combines the functionality of both a Service Oriented Architecture (S0A) and Event Driven Architecture (EDA) to achieve an agile, enterprise ESB.

As previously stated, ServiceMix is an open source ESB that is based on the Java Business Integration (JBI) standard. These two factors, open source and open standards-based, allow for low entry cost, maximum flexibility, reuse, and investment protection.

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Reuse and investment protection also results from the adherence to standards. Not only can developers swap out ESB components, or use components in another JBI-standard ESB, but they can swap out the entire ESB and still use the standard plug-in components.

As an agile ESB, ServiceMix allows plug-in services which can combine to create a service oriented architecture. ServiceMix allows these services to operate in an event driven way as well. In other words, the services are decoupled and listen on the bus for service requests. The bus is responsible for quality of service (QoS) features such as message persistence, guaranteed delivery, failure handling, and transaction support.

ServiceMix supports event driven architecture for events occurring both internal and external to the bus. In other words, JMS binding components can listen for the arrival of messages, i.e., the "event" on topics or queues which are external to the bus, while other binding components and service engine components can listen for
messages on the normalized message bus.

While decoupled (EDA) operation (as described in the previous two paragraphs) is more appropriate for the scalability and reliabilty required for high transaction production environments, synchrounous synchronous request/response communication found in early SOA implementations, is also supported. ThereforeThus, ServiceMix effectively combines SOA and EDA for the development and deployment of composite enterprise applications.

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