Integration Technologies - Guide to Cloud Computing for Business and Technology Managers - page 131

An ESB also provides control over the deployment, usage, and maintenance
of services. This allows logging, profiling, load balancing, performance tun-
ing, charging for service use, distributed deployment, on-the-fly reconfigu-
ration, etc. Other important management features include the definition of
correlation between messages, definition of reliable communication paths,
and definition of security constraints related to messages and services.
An ESB should make services broadly available. This means that it should
be easy to find, connect, and use a service irrespective of the technology it
is implemented in. With broad availability of services, an ESB can increase
reuse and can make the composition of services easier. Finally, an ESB should
provide management capabilities, such as message routing, interaction, and
transformation, which we have already described.
5.12 Enterprise Systems
There are many issues to deal with in enterprise integration, but at the core is
an architectural problem concerning modifiability. Consider enterprise has
“n” number of different business applications that need integrating to sup-
port some new business processes that may entail communicating between
these “n” applications using their published messaging interfaces. Assuming
one-way messages only, this means the business process under consideration
must be able to transform its source data into the remaining (n - 1) different
message formats (this direct dependency creates a tight coupling between
these applications); but this does not end here; similar changes may be
necessitated in other applications leading to requirement for corresponding
number of interfaces. In the general case, the number of interfaces between
N applications is N × (N - 1)/2. So as N grows, the number of possible inter-
faces grows exponentially, making such point-to-point architectures nons-
calable in terms of modifiability. Considering that many interfaces between
two applications are two way, requiring two transformations, and most
applications have more than one interface, so in reality, the number of inter-
faces between N tightly coupled applications can be considerably greater
than N(N - 1)/2. This results in a highly complex architecture.
5.12.1 Replacing a Point-to-Point Integration Architecture with a Broker
An introduction of a message broker as an intermediatory between the
applications can reduce the complexity dramatically. Complexity in the inte-
gration end points, namely, the business applications, is greatly reduced as
they just send messages using their native formats to the broker, and these
are transformed inside the broker to the required destination format. If there
is a need to change an end point, then one just needs to modify the message