Probably the most dominant architectural pattern used to implement the middle-tier for service-oriented architectures is the Enterprise Service Bus (ESB). This pattern works particularly well when the number of service consumers is limited and their behavior is predictable. A typical example would be building an ESB for services within one enterprise, where the service providers and consumers are well known, predictable, and are limited in number.

On the next few pages we'll present and analyze a use case of a trading firm, which will require building an Enterprise Service Bus.