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Cohesion (computer science)
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<p>In <a href="/facts/Computer_programming/QmSsFnu0">computer programming</a>, cohesion refers to the <i>degree to which the elements inside a <a href="/facts/Module_(programming)/sNoqKvRD">module</a> belong together</i>. In one sense, it is a measure of the strength of relationship between the <a href="/facts/Method_(computer_programming)/8kAXxVYs">methods</a> and data of a <a href="/facts/Class_(computer_programming)/zvzkSAtE">class</a> and some unifying purpose or concept served by that class. In another sense, it is a measure of the strength of relationship between the class's methods and data. </p><p>Cohesion is an <a href="/facts/Level_of_measurement/8GAxPxFv">ordinal</a> type of measurement and is usually described as “high cohesion” or “low cohesion”. Modules with high cohesion tend to be preferable, because high cohesion is associated with several desirable software traits including <a href="/facts/Robustness_(computer_science)/jHr1dT3m">robustness</a>, reliability, <a href="/facts/Reusability/te10mWEI">reusability</a>, and understandability. In contrast, low cohesion is associated with undesirable traits such as being difficult to maintain, test, reuse, or understand. </p><p>Cohesion is often contrasted with <a href="/facts/Coupling_(computer_science)/QEeSaXF3">coupling</a>. High cohesion often correlates with <a href="/facts/Loose_coupling/uXRb4qBJ">loose coupling</a>, and vice versa. The <a href="/facts/Software_metric/kus08fbs">software metrics</a> of coupling and cohesion were invented by <a href="/facts/Larry_Constantine/advmm0KF">Larry Constantine</a> in the late 1960s as part of <a href="/facts/Structured_Design/ejVb0w2v">Structured Design</a>, based on characteristics of “good” programming practices that reduced maintenance and modification costs. Structured Design, cohesion and coupling were published in the article <i>Stevens, Myers & Constantine</i> (1974) and the book <i>Yourdon & Constantine</i> (1979). The latter two subsequently became standard terms in <a href="/facts/Software_engineering/KX6cE9kz">software engineering</a>. </p>