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functional cohesion
subject			fact

functional cohesion	has definition A form of cohesion in which modules which together perform a function (a computation that returns a result and has no side effects) are kept together, and everything else is kept out
	has advantages It is easier to understand a module when you know all it does is generate one specific output and has no side effects It is easier to replace a functionally cohesive module with another that performs the same computation functionally cohesive module is much more likely to be reusable
	is a subtopic of 9.2 - Principles Leading to Good Design
	is achieved when a module only performs a single computation, and returns a result, without having side-effects
	is a kind of cohesion
	should be used if possible
cohesion	has precedence table Cohesion type Comments functional cohesion If an aspect of a design can be achieved using a functionally cohesive module then it is normally best to do so. layer cohesion Layer cohesion should typically have higher priority. Dividing systems into layers has been shown to considerably simplify systems. communicational cohesion Communicational cohesion, as embodied in the classes of an object oriented system, should have high priority. Here we list it below layer cohesion since modules may access the same kind of data in different layers. sequential cohesion Sequential cohesion is effectively a strong form of temporal cohesion, but is weaker than communicational cohesion since different data types may be involved in the different stages of a sequentially cohesive module. temporal cohesion Temporal cohesion should typically be considered weaker than other types of cohesion. It is important, but only if the other types of cohesion have been achieved. utility cohesion Utility cohesion is the weakest kind of cohesion since it serves to group together those parts of the system that do not seem to logically belong anywhere else.
software quality	is hard to assess