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In computing, an enterprise service bus (ESB) refers to a software architecture construct. This construct is typically implemented by technologies found in a category of middleware infrastructure products, usually based on recognized standards, which provide foundational services for more complex architectures via an event-driven and standards-based messaging engine (the bus). For the formal concept of computation, see computation. ... The software architecture of a program or computing system is the structure or structures of the system, which comprise software elements, the externally visible properties of those elements, and the relationships between them. ... This article is about integration software. ...

An ESB generally provides an abstraction layer on top of an implementation of an enterprise messaging system, which allows integration architects to exploit the value of messaging without writing code. Contrary to the more classical enterprise application integration (EAI) approach of a monolithic stack in a hub and spoke architecture, the foundation of an enterprise service bus is built of base functions broken up into their constituent parts, with distributed deployment where needed, working in harmony as necessary. An enterprise messaging system (EMS) is a set of published Enterprise-wide standards that allows organizations to send semantically precise messages between computer systems. ... Enterprise Application Integration (EAI) is defined as the uses of software and computer systems architectural principles to integrate a set of enterprise computer applications. ... The Spoke-hub distribution paradigm derives its name from a bicycle wheel, which consists of a number of spokes jutting outward from a central hub. ...

ESB does not implement a service-oriented architecture (SOA) but provides the features with which one may be implemented. Although it is a common belief, ESB is not necessarily web-services based^{[citation needed]}. ESB should be standards-based and flexible, supporting many transport mediums. Based on EAI rather than SOA patterns, it tries to remove the coupling between the service called and the transport medium. Service Oriented Architecture (SOA) is an architectural style that guides all aspects of creating and using business processes, packaged as services, throughout their lifecycle, as well as defining and provisioning the IT infrastructure that allows different applications to exchange data and participate in business processes regardless of the operating systems... Web services architecture The W3C defines a Web service (many sources also capitalize the second word, as in Web Services) as a software system designed to support interoperable Machine to Machine interaction over a network. ...

Most ESB providers now build ESBs to incorporate SOA principles and increase their sales, e.g. Business Process Execution Language (BPEL). Business Process Execution Language (or BPEL, pronounced bipple, bepple or bee-pell), is a business process modeling language that is executable. ...

What is an Enterprise Service Bus?

There is some disagreement on whether an enterprise service bus is an architectural style, a software product, or a group of software products. While use of an ESB certainly implies adherence to a particular architecture, the term "enterprise service bus" is almost always used to denote the software infrastructure that enables such an architecture.

ESB Architecture

The word "bus" is a reference to the physical bus that carries bits between devices in a computer. The enterprise service bus serves an analogous function at a higher level of abstraction. In an enterprise architecture making use of an ESB, an application will communicate via the bus, which acts as a message broker between applications. The primary advantage of such an approach is that it reduces the number of point-to-point connections required to allow applications to communicate. This, in turn, makes impact analysis for major software changes simpler and more straightforward. By reducing the number of points-of-contact to a particular application, the process of adapting a system to changes in one of its components becomes easier. PCI Express bus card slots (from top to bottom: x4, x16, x1 and x16), compared to a traditional 32-bit PCI bus card slot (bottom) In computer architecture, a bus is a subsystem that transfers data or power between computer components inside a computer or between computers, and a bus... This article is about the concept of abstraction in general. ... This article is about Enterprise Architecture. ... Message broker is an intermediary program that translates a message from the formal messaging protocol of the sender to the formal messaging protocol of the receiver in a telecommunication network where programs communicate by exchanging formally-defined messages. ...

ESB as Software

In such a complex architecture, the ESB is the piece of software that lies between the business applications and enables communication among them. Ideally, the ESB should be able to replace all direct contact with the applications on the bus, so that all communication takes place via the bus. In order to achieve this objective, the bus must encapsulate the functionality offered by its component applications in a meaningful way. This is typically accomplished through the use of an enterprise message model. The message model defines a standard set of messages that the ESB will both transmit and receive. When it receives a message, it routes it to the appropriate application. Often, owing to the fact that the application was not built with the message model in mind, the ESB will have to transform the message into a legacy format that is understandable by the application. The software responsible for affecting these transformations is referred to as an adapter (analogous to a physical adapter). It is not widely agreed whether these adapters should be considered part of the ESB or not. In computer science, the principle of information hiding is the hiding of design decisions in a computer program that are most likely to change, thus protecting other parts of the program from change if the design decision is changed. ... This mains power plug travel adaptor allows European or British plugs to be inserted into American or Australian sockets An adapter or adaptor is a device used to match the physical or electrical characteristics of two different things so that a connection may be made between them. ...

The connection between the enterprise message model and the functionality offered by the applications is crucial. If the message model does not completely encapsulate the applications' functionality, then other applications that desire that functionality will be forced to bypass the bus and invoke the applications directly. Doing so violates all of the principles outlined above, and negates many of the advantages of using an ESB.

Further description of an ESB is difficult because it is neither a single product nor a formal standard. To provide further details about the behavior and nature of an ESB necessarily requires using generalities. ESBs are typically built around the exchange of XML messages. (As such, the enterprise message model is defined in terms of a series of XML Schema definitions describing the set of legal messages.) While Web Services are not used exclusively, their use is common, and the message exchange is almost always done in a platform-independent manner. This allows the ESB to integrate applications that run on a variety of mainframe and client-server operating systems. The Extensible Markup Language (XML) is a general-purpose markup language. ... An XML schema is a description of a type of XML document, typically expressed in terms of constraints on the structure and content of documents of that type, above and beyond the basic syntax constraints imposed by XML itself. ... Web services architecture The W3C defines a Web service (many sources also capitalize the second word, as in Web Services) as a software system designed to support interoperable Machine to Machine interaction over a network. ... Mainframe may refer to one of the following: Mainframe computer, large data processing systems Mainframe Entertainment, a Canadian computer animation and design company. ... Client/Server is a network application architecture which separates the client (usually the graphical user interface) from the server. ...

Salient characteristics

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"Enterprise Service Bus" is a convenient catch-all term for a set of capabilities, which can be implemented in different ways. There is considerable debate on whether an ESB is a tangible product or an architectural style, and on exactly how an ESB may be implemented (e.g., centralised (broker or hub) versus decentralised (smart endpoints)). For example, some SOA practitioners claim that SOAP + WS-Addressing is the Bus. In any case, certain core capabilities are generally accepted as being functions of an ESB: Image File history File links Question_book-3. ... For other uses, see Soap (disambiguation). ... WS-Addressing is a specification of transport-neutral mechanisms that allow web services to communicate addressing information. ...

¹ Some do not consider Process Choreography to be an ESB function. It has been suggested that this article or section be merged into Event Stream Processing. ... Business Activity Monitoring (BAM) is software that aids in monitoring of business processes, as those processes are implemented in computer systems. ...

² While Process Choreography supports implementation of complex business processes that require coordination of multiple business services (usually using BPEL), Service Orchestration enables coordination of multiple implementation services (most suitably exposed as an aggregate service) to serve individual requests. A business process language known as Business Process Execution Language (BPEL), which supersedes WSFL and is serialized in XML, aims to enable programming in the large. ...

In addition, an ESB is expected to exhibit the following characteristics:

• It is usually operating-system and programming-language agnostic; for example, it should enable interoperability between Java and .NET applications.
• It uses XML (eXtensible Markup Language) as the standard communication language.
• It supports web-services standards.
• It supports various MEPs (Message Exchange Patterns) (e.g., synchronous request/response, asynchronous request/response, send-and-forget, publish/subscribe).
• It includes adapters for supporting integration with legacy systems, possibly based on standards such as JCA
• It includes a standardized security model to authorize, authenticate and audit use of the ESB.
• To facilitate the transformation of data formats and values, it includes transformation services (often via XSLT or XQuery) between the format of the sending application and the receiving application.
• It includes validation against schemas for sending and receiving messages.
• It can uniformly apply business rules, enriching messages from other sources, the splitting and combining of multiple messages and the handling of exceptions.
• It can provide a unified abstraction across multiple layers
• It can route or transform messages conditionally, based on a non-centralized policy (i.e. no central rules-engine needs to be present).
• It supports queuing, holding messages if applications are temporarily unavailable.

Java language redirects here. ... Microsoft . ... The Extensible Markup Language (XML) is a W3C-recommended general-purpose markup language that supports a wide variety of applications. ... hello world. ... J2EE Connector Architecture (JCA) is Java-based technology solution for connecting application servers and enterprise information systems (EIS) as part of enterprise application integration (EAI) solutions. ... Diagram of the basic elements and process flow of Extensible Stylesheet Language Transformations. ... XQuery is a query language (with some programming language features) that is designed to query collections of XML data. ...

Key benefits

• Faster and cheaper accommodation of existing systems.
• Increased flexibility; easier to change as requirements change.
• Standards-based.
• Scales from point solutions to enterprise-wide deployment (distributed bus).
• Predefined ready-for-use service types.
• More configuration rather than integration coding.
• No central rules engine, no central broker.
• Incremental changes can be applied with zero down-time; enterprise becomes "refactorable". ^{(please cite reference or explain this.)}

Key disadvantages

• Enterprise Message Model is usually required, resulting in additional management overhead. May not be a simple task to achieve many disparate systems collaborating on message standards.
• Requires ongoing management of message versions to ensure the intended benefit of loose coupling. Incorrect, insufficient, or incomplete management of message versions can result in tight coupling instead of the intended loose coupling.
• It normally requires more hardware than simple point to point messaging.
• New skills needed to configure, manage, and operate an ESB.
• Extra overhead and increased latency caused by messages traversing the extra ESB layer, especially as compared to point to point communications.
• Some critics remark that ESB require a significant effort to implement, but produces no value unless SOA services are subsequently created for the ESB.^[1]

In computer science, coupling or dependency is the degree to which each program module relies on each one of the other modules. ...

See also

• Enterprise Integration Patterns
• Java Business Integration
• Service-oriented architecture
• Business Process Management
• Universal Integration Platform
• Comparison of Business Integration Software
• Enterprise application integration
• Service-Oriented Architecture Implementation Framework
• Business Service Provider
• Message Oriented Middleware
• Complex Event Processing
• Event Stream Processing
• Service-Oriented Modeling

Enterprise Integration Patterns:http://www. ... Java Business Integration (JBI) is a specification developed under the Java Community Process (JCP) for an approach to implementing a service-oriented architecture (SOA). ... Service Oriented Architecture (SOA) is an architectural style that guides all aspects of creating and using business processes, packaged as services, throughout their lifecycle, as well as defining and provisioning the IT infrastructure that allows different applications to exchange data and participate in business processes regardless of the operating systems... Business Process Management (BPM) is a field of knowledge at the intersection between management and information technology, encompassing methods, techniques and tools to design, enact, control, and analyze operational business processes involving humans, organizations, applications, documents and other sources of information. ... A Universal Integration platform is a development and/or configuration time analog of a Universal Server. ... This article is a comparison of business integration and business process automation software. ... Enterprise Application Integration (EAI) is defined as the uses of software and computer systems architectural principles to integrate a set of enterprise computer applications. ... Service-oriented architectures (SOA) are based on the notion of software services, which are high-level software components that include Web services. ... Business service providers (BSPs) are companies that offer state-of-the-art business applications over the Web. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... It has been suggested that this article or section be merged into Event Stream Processing. ... It has been suggested that Complex Event Processing be merged into this article or section. ... Service-oriented Modeling (SOM) to produce a Service-oriented Architecture (SOA) is referred to as SOMA (Service-oriented Modeling and Architecture). ...

Books

• Dave Chappell, "Enterprise Service Bus" (O’Reilly: June 2004, ISBN 0-596-00675-6)
• Binildas A. Christudas, "Service Oriented Java Business Integration" (Packt Publishers: Feb 2008, ISBN 1847194400; ISBN 13 978-1-847194-40-4)
• Michael Bell, "Service-Oriented Modeling: Service Analysis, Design, and Architecture" (2008 Wiley & Sons, ISBN 978-0-470-14111-3)

References

1. ^ ESB-Oriented Architectures considered harmful

External links

• The Role of the Enterprise Service Bus (InfoQ - Video Presentation) (October 23, 2006)
• ESB Roundup Part One: Defining the ESB (InfoQ) (July 13, 2006)
• ESB Roundup Part Two: Use Cases (InfoQ) (July 05, 2006)
• JSR-208: Java Business Integration (August 2005)
• Enterprise service buses hit the road : Infoworld Test Center (July 22, 2005)
• "Lasting concept or latest buzzword?" (Nicolas Farges, 2003)
• "Services Fabric—Fine Fabrics for New Era Systems" (Binildas A. Christudas, 2007)
• "What is ESB?" (June 4, 2004)
• "ESBs in 2007: Taking the Open Source Bus to SOA" (Dennis Byron, September 20, 2007)
• Aggregate Services in ServiceMix JBI ESB : PACKT Publishers (Binildas A. Christudas, November 30, 2007)
• JBoss ESB
• Mule (software) an Open Source ESB and integration platform.
• Open source ESB. (February 2008)