Enterprise Application Integration (EAI) - Guide to Cloud Computing for Business and Technology Managers - page 105

The spoke-hub integration is effectively implemented by message broker
software that translates messages from one protocol to another, making sure
that the data structures are compatible. Message brokers allow the rules of
communication between applications to be defined outside the applications
so that application developers do not need to worry about designing adaptors
for every other application. When a message is received, the message broker
runs the rule over the received message, transforms the data if needed, and
inserts it into the appropriate queue. The rules are defined in a declarative
way based on the communication protocols used by the applications. The
message broker uses these rules to identify the message queues where the
messages should be relayed. Publish/Subscribe software architecture style
can be used to implement message brokers. Accordingly, applications pub-
lish their messages that are then relayed to the receiving applications that
subscribe to them.
The major drawback of the message broker approach is the difficulty in
managing and configuring the rules when the dependencies between appli-
cations are complex. Also, because message-based communications are
inherently asynchronous, the solution may not be well suited for synchro-
nous communication requirements, such as real-time computing or near-
real-time computing.
4.3 Summary
This chapter focuses on enterprise applications and aspects related to the
integration of applications. It describes the basics and models of integration
including presentation, functional, data, business process, and bussiness-to-
bussiness integration. The last part of the chapter explains the various pat-
terns of integration, which will be used in Chapter 5.