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cohesion
subject			fact

cohesion	has definition A measure of the extent to which related aspects of a system are kept together in the same module, and unrelated aspects are kept out
	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.
	is a subtopic of 9.2 - Principles Leading to Good Design
	is a kind of measurement
	is a kind of software quality
software quality	is hard to assess

Kinds of cohesion :

• communicational cohesion (5 facts) - A form of cohesion in which procedures that access the same data are kept together
• functional cohesion (6 facts) - 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
• layer cohesion (7 facts) - A form of cohesion in which the facilities for providing or accessing a set of services through an API or hardware interface are kept together. There must also be a strict hierarchy in which higher level layers can access only lower-level layers. In other words, the system is effectively divided into layers
• procedural cohesion (5 facts) - A form of cohesion in which procedures that are called one after another are kept together
• sequential cohesion (7 facts) - A form of cohesion in which a series of procedures, where one provides input to the next, are kept together
• temporal cohesion (7 facts) - A form of cohesion in which aspects of a system are grouped together which are used during the same phase of execution of a program, i.e. execute close together in time
• utility cohesion (4 facts) - A form of cohesion in which utilities which cannot be logically placed in other cohesive units are kept together