Cohesion

Updated 06 Sep 2026

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def
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  a measure of the functional strength of a module
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  a component or class encapsulates only attributes and operations closely related to one another and to the component itself
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goal
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  keep cohesion as high as possible — high cohesion means a module does one thing well
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kinds of cohesion (ranked highest/best to lowest/worst)
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  functional — different elements cooperate to achieve a single function ← best
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  sequential — output from one element is input to the next
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  communicational — all functions reference or update the same data structure
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  procedural — all functions are part of a procedure requiring steps in sequence
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  temporal — all functions must be executed in the same time span
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  logical — all elements perform similar operations (e.g., all error-handling routines)
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  coincidental — elements relate to each other very loosely, if at all ← worst
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relation to design quality
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  good design: high cohesion and low Coupling → functional independence
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  a functionally independent module performs a single task with minimal interaction with other modules
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related
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Cards
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  What does high cohesion mean for a module?
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    the module has one clear, specific responsibility, and everything inside it supports that single purpose

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