Vertical Integration (as opposed to
"horizontal") is the process of integrating subsystems according to
their functionality by creating functional entities also referred to as
silos.[7] The benefit of this method is that the integration is performed
quickly and involves only the necessary vendors, therefore, this method is
cheaper in the short term. On the other hand, cost-of-ownership can be
substantially higher than seen in other methods, since in case of new or
enhanced functionality, the only possible way to implement (scale the system)
would be by implementing another silo. Reusing subsystems to create another
functionality is not possible.[8]
Star Integration or also known as Spaghetti
Integration is a process of integration of the systems where each system is
interconnected to each of the remaining subsystems. When observed from the
perspective of the subsystem which is being integrated, the connections are
reminiscent of a star, but when the overall diagram of the system is presented,
the connections look like spaghetti, hence the name of this method. The cost
varies due to the interfaces which subsystems are exporting. In a case where
the subsystems are exporting heterogeneous or proprietary interfaces, the
integration cost can substantially rise. Time and costs needed to integrate the
systems increase exponentially when adding additional subsystems. From the
feature perspective, this method often seems preferable, due to the extreme
flexibility of the reuse of functionality.[8]
Horizontal Integration or Enterprise Service Bus (ESB)
is an integration method in which a specialized subsystem is dedicated to
communication between other subsystems. This allows cutting the number of
connections (interfaces) to only one per subsystem which will connect directly
to the ESB. The ESB is capable of translating the interface into another
interface. This allows cutting the costs of integration and provides extreme
flexibility. With systems integrated using this method, it is possible to
completely replace one subsystem with another subsystem which provides similar
functionality but exports different interfaces, all this completely transparent
for the rest of the subsystems. The only action required is to implement the
new interface between the ESB and the new subsystem.[8]
The horizontal
scheme can be misleading, however, if it is thought that the cost of
intermediate data transformation or the cost of shifting responsibility over
business logic can be avoided.[8]
A common data format is an integration method to avoid
every adapter having to convert data to/from every other applications' formats,
Enterprise application integration (EAI) systems usually stipulate an
application-independent (or common) data format. The EAI system usually
provides a data transformation service as well to help convert between
application-specific and common formats. This is done in two steps: the adapter
converts information from the application's format to the bus's common format.
Then, semantic transformations are applied on this (converting zip codes to city
names, splitting/merging objects from one application into objects in the other
applications, and so on).
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