An enterprise service bus (ESB) implements a communication system between mutually interacting software applications in a service-oriented architecture (SOA). It represents a software architecture for distributed computing, and is a special variant of the more general client-server model, wherein any application may behave as server or client. ESB promotes agility and flexibility with regard to high-level protocol communication between applications. Its primary use is in enterprise application integration (EAI) of heterogeneous and complex service landscapes. Architecture The concept of the enterprise service bus is analogous to the bus concept found in computer hardware architecture combined with the modular and concurrent design of high-performance computer operating systems. The motivation for the development of the architecture was to find a standard, structured, and general purpose concept for describing implementation of loosely coupled software components (called services) that are expected to be independently deployed, running, heterogeneous, and disparate within a network. ESB is also a common implementation pattern for service-oriented architecture, including the intrinsically adopted network design of the World Wide Web. No global standards exist for enterprise service bus concepts or implementations. Most providers of message-oriented middleware have adopted the enterprise service bus concept as de facto standard for a service-oriented architecture. The implementations of ESB use event-driven and standards-based message-oriented middleware in combination with message queues as technology frameworks. However, some software manufacturers relabel existing middleware and communication solutions as ESB without adopting the crucial aspect of a bus concept. Functions An ESB applies the design concept of modern operating systems to independent services running within networks of disparate and independent computers. Like concurrent operating systems, an ESB provides commodity services in addition to adoption, translation and routing of client requests to appropriate answering services. The primary duties of an ESB are: Route messages between services Monitor and control routing of message exchange between services Resolve contention between communicating service components Control deployment and versioning of services Marshal use of redundant services Provide commodity services like event handling, data transformation and mapping, message and event queuing and sequencing, security or exception handling, protocol conversion and enforcing proper quality of communication service. History The first published usage of the term "enterprise service bus" is attributed to Roy W. Schulte from the Gartner Group 2002 and the book The Enterprise Service Bus by David Chappell. Although a number of companies take credit for coining the phrase, in an interview, Schulte said that the