Web Services Message Routers
Message routers direct data from a requesting resource to a responding resource and back. These are also known as data routers, application brokers, or message brokers.
Message routers are a way to reduce complexity. When there is a need to exchange messages or data among internal systems, the number of possible interations can become complex. This is illustrated in the figure below where each internal system needs to exchange messages or data with all the other internal systems.
A message router simplifies the system architecture by being able to route messages and data to the correct internal system. This reduces the number of interconnections in the systems architecture as illustrated in the following figure.
Existing internal systems will most likely also need an adapter. See Web Services Adapters.
More information on Web Services message routers can be found in Web Services, Service-Oriented Architectures, and Cloud Computing: The Savvy Manager's Guide.
More on the general topic: Messaging Components