Coupling and cohesion were defined in the 1970s by Larry Constantine and Edward Yourdon. They are the best ways we know of measuring the inherent maintainability and adaptability of a software system. In short, coupling is a measure of how interrelated two software components are. Cohesion is a measure of how related the functions performed by a software component are. We want to strive for low coupling and high cohesion. High coupling implies that, when we change a component, changes to other components are likely. Low cohesion implies difficulty in isolating the causes of errors or places to adapt to meet new requirements. Constantine and Yourdon even provided a simple-to-use way to measure the two concepts. Learn it. Use the measure to guide your design decisions.
You want:
- low coupling
- high cohesion
The image above is a special forces team that gives an alternative example of low coupling with high cohesion. The sniper team is another such example.
