Where does coupling collide?

The degree to which one software module depends on the internals of another, so that a change in one forces a change in the other. In Structured Design (1974) Stevens, Myers, and Constantine paired coupling with cohesion and argued that good design keeps coupling low and cohesion high: modules should connect through narrow, well-defined interfaces rather than through shared data or hidden assumptions. The referent is a relationship between two units of code, and its unit is the strength of one dependency, judged by how much one module must know about another. What sets this meaning apart is that low coupling is a design goal, something an engineer works to reduce, not a fact of nature and not a reaction to be run.[1]

Unit

The strength of one dependency between two code modules

Recovery means

Not applicable

Measured by

Judged qualitatively by coupling type, or by dependency metrics such as fan-in and fan-out

The strength with which two physical systems influence each other, so that the motion or state of one enters the equations of the other. In Classical Mechanics Goldstein, Poole, and Safko treat coupled oscillators through the terms that link their coordinates, and the size of that link, the coupling constant, sets how strongly energy passes between them and where the normal modes fall. More broadly a coupling constant fixes the strength of an interaction, such as the charge that governs the electromagnetic force. The referent is a physical interaction, and its unit is a coefficient in the dynamics. Unlike the software meaning, coupling here is neither good nor bad and nothing to reduce: it is a measured quantity that describes how nature is put together.[2]

Unit

A coefficient setting the interaction strength between two systems

Recovery means

Not applicable

Measured by

Read off as a coupling constant from the equations of motion, spectra, or scattering

A reaction that joins two molecular fragments into one, forming a new bond between them, usually under the action of a metal catalyst. In their 1995 review Miyaura and Suzuki set out how palladium catalysis couples an organoboron compound with an organic halide to build a carbon-carbon bond, a method now central to making complex molecules. The referent is a chemical transformation, and its unit is one coupling event that stitches two pieces together. This meaning parts most sharply from the others because coupling is an action, not a standing property: it names something a chemist makes happen in a flask, an event with a yield and a mechanism, rather than a degree of dependence or a coefficient that simply holds.[3]

Unit

One reaction that joins two molecular fragments into a new bond

Recovery means

Not applicable

Measured by

Reaction yield, selectivity, and rate for the coupling step

The degree to which the elements of an organization are linked, where loose coupling means they respond to each other yet keep their own identity, logic, and separateness. In his 1976 account of educational organizations as loosely coupled systems, Weick argued that a school's parts, its offices, classrooms, and rules, are joined weakly and occasionally rather than tightly, which lets each adapt on its own and buffers the whole against local shocks. The referent is the linkage between social units, and its unit is how tightly two elements move together. Unlike the physics meaning, loose coupling here is often a virtue: the slack that looks like poor connection is what gives an organization room to absorb trouble and change in one place without upheaval everywhere.[4]

Unit

How tightly two organizational elements are linked

Recovery means

Not applicable

Measured by

Inferred from how responsive yet distinct two organizational elements remain