Enterprise Service Bus (ESB)
The characteristics of ESB are as follows:
The ESB is not just a transformation engine. While transformation is a core function of an ESB, it is not the only thing it does.
Its biggest value is to match and route messages and services, to convert between transport protocols and to manage and distribute business events. The idea of describing an ESB as a ‘proxy’ might be new to some people, but the message resonates well with customers.
Here the key point is that by having a proxy, you do not need to ‘hard-code’ connectivity logic directly into applications. This makes the application logic much more modular and allows you to swap out other applications according to the requirements. 
