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principles:high_cohesion

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High Cohesion (HC)

Variants and Alternative Names

Context

Definition

Cohesion in a module should be high.

Description

The cohesion of a module is a measure for how well the internal parts of a module (e.g. the methods and attributes of a class) belong together. Having a high cohesion means, that a module should only comprise responsibilities which belong together.

Several kinds of cohesion can be distinguished some of which are strong and some of which are loose. So strong forms of coupling should be preferred: FIXME add explanation of cohesion types

Rationale

Not adhering to this principle, i.e. having a low cohesion, means that one module has several unrelated or only loosely related responsibilities. A change in the requirements for one of these may thus also affect the others which would not be the case in a highly cohesive module.

Origin

Evidence

Relations to Other Principles

Generalizations

Specializations

Contrary Principles

  • Keep It Simple Stupid: Sometimes it is simpler to assign a minor unrelated responsibility to a module, which lowers the cohesion. On the other hand introducing a new module for the responsibility would be better in terms of cohesion but increases complexity as it increases the number of modules.

Complementary Principles

Principle Collections

OOD Principle Language
General Principles
ML KISS MIMC DRY GP RoE
Modularization Principles
MP HC ECV
Module Communication Principles
TdA/IE LC DIP
Interface Design Principles
EUHM PLS UP
Internal Module Design Principles
IH/E IAP LSP PSU

Example

Description Status

Further Reading

principles/high_cohesion.1355780757.txt.gz · Last modified: 2013-05-20 12:45 (external edit)