CSC/ECE 517 Fall 2007/wiki2 7 an

Cohesion and coupling. Cohesion and coupling are concepts that are reasonably easy to understand, but nonetheless, it is challenging to find good examples that are succinct. Browse the hundreds of Web pages that attempt to explain these concepts, picking your favorite examples. Many of these pages mention related concepts; list some of them and explain how they relate to cohesion and coupling. Be sure to mention the metrics that can be used to measure how well a program conforms to the principles of high cohesion and low coupling.

What is coupling?

Coupling is the degree to which each program module relies on each one of the other modules. Unnecessary object coupling needlessly decreases the reusability of the coupled objects and also increases the chances of system corruption when changes are made to one or more of the coupled objects.

Thus the design goal is to minimize coupling and improve reusability. Coupling is broadly divided into two types-low coupling and high coupling. Low coupling refers to a relationship in which one module interacts with another module through a stable interface and does not need to be concerned with the other module's internal implementation With low coupling, a change in one module will not require a change in the implementation of another module. Low coupling is often a sign of a well-structured computer system, and when combined with high cohesion, supports the general goals of high readability and maintainability.

On the other hand, systems with high coupling face the following problems

• Change in one module forces a ripple of changes in other modules. • Modules are difficult to understand in isolation. • Modules are difficult to reuse or test because dependent modules must be included.

Thus it is evident that low coupling tends to produce reusable methods. But it is also not possible to write completely decoupled methods since the program will not work.

Types of coupling