Enterprise Application Integration (EAI) - Guide to Cloud Computing for Business and Technology Managers - page 104

become unmanageable as the number of applications silos increases: if there
are N applications to be integrated, then the number of interfaces to be devel-
oped becomes N × N; that is, the number of interfaces to be developed grows
on the order of N 2 .
Another problem with point-to-point integration is the inability to respond
to changes quickly. This is because the interfaces are hardwired to the appli-
cation pairs, and changes within the enterprise information infrastructure
may require rewiring the interfaces.
4.2.3.2 Message-Oriented Integration
In message-oriented integration solutions, the applications communicate
with each other by sending and receiving messages through a middle-
ware that manages the message queue associated with each application.
Integration of two applications is by sending and receiving messages to the
appropriate queue and the middleware ensures that the messages are deliv-
ered. However, point-to-point aspect of the integration is not eliminated,
since applications are required to specify the recipients of the messages.
4.2.3.3 Hub-Spoke Integration
Spoke-hub integration eliminates the need to encode the address of the
recipient. A centralized enterprise application middleware routes messages
to their destinations based on the content and the format of the message. All
applications are connected to the central integration hub like the spokes on
a bicycle wheel. For this reason, this integration style is called spoke-hub
integration. The concept is effectively used in many industries, such as trans-
portation and telecommunication.
A collection of point-to-point integrations with one common end
results effectively in a hub-spoke integration pattern.
Spoke-hub integration reduces the number of connections from order of N 2
to N. This means that only as many interfaces as the number of applications
need to be developed. In practice, a centralized integration hub provides a
place for the adapters and it is the responsibility of the application developer
to provide an adapter for each hub they connect to. Without standardiza-
tion of adapters, this requires some development and testing resources (see
Chapter 5, Section 5.12.1, “Replacing a Point-to-Point Integration Architecture
with a Broker”).