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Services are loosely coupled
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No one can predict how an IT environment will evolve. How automation solutions grow, integrate, or are replaced over time can never be accurately planned out because the requirements that drive these changes are almost always external to the IT environment.
Being able to ultimately respond to unforeseen changes in an efficient manner is a key goal of applying service-orientation. Realizing this form of agility is directly supported by establishing a loosely coupled relationship between services.
 Services limit dependencies to the service contract, allowing underlying provider and requestor logic to remain loosely coupled.
Loose coupling is a condition wherein a service acquires a knowledge of another service while still remaining independent of that service. Loose coupling is achieved through the use of service contracts (service descriptions) that allow services to interact within predefined parameters.
It is interesting to note that within a loosely coupled architecture, service contracts actually tightly couple operations to services. Once a service is formally described as being the location of an operation, other services will depend on that operation-to-service association.
This page contains excerpts from:
Service-Oriented Architecture:
Concepts, Technology, and Design
by Thomas Erl
(ISBN: 0131858580, Prentice Hall/PearsonPTR, Hardcover, 792 pages).
For more information, visit www.soabooks.com.
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