What is Coupling? What is Cohesion? Explain different types of Cohesion and Coupling with proper example.

Understanding Coupling and Cohesion in Software Engineering

Coupling refers to the degree of interdependence between modules or classes in a software system.
High coupling indicates strong dependencies, making changes difficult and increasing the risk of unintended consequences.
Low coupling promotes modularity, reusability, and maintainability.

Content Coupling: One module directly modifies data within another. Example: Module A directly changing variables inside Module B. This is extremely undesirable.
Common Coupling: Modules share global data. Example: Multiple modules accessing and modifying the same global variable. Difficult to manage and understand.
Control Coupling: One module controls the flow of execution in another using flags or parameters. Example: Module A passing a flag to Module B to dictate its behavior. Often avoidable through better design.
Stamp Coupling: Modules share a composite data structure, but only use a portion of it. Example: Passing a large object when only a small subset of its data is needed. Inefficient and leads to tight coupling.
Data Coupling: Modules communicate through passing data parameters. Example: Module A passing specific data values to Module B. The most desirable form of coupling.

Cohesion refers to how closely related the functions within a single module or class are.
High cohesion implies that a module performs a single, well-defined task.
Low cohesion suggests that a module performs unrelated tasks, making it difficult to understand, maintain, and reuse.

Coincidental Cohesion: Parts of a module have no logical relationship. Example: A module containing unrelated functions such as logging and database access. Weakest form of cohesion.
Logical Cohesion: A module performs multiple related functions, but each is invoked independently. Example: A module performing several validation operations. Slightly improved over coincidental, but still weak.
Temporal Cohesion: Functions within a module are grouped because they are executed at the same time. Example: A module containing functions that are all executed during system initialization. Better than logical, but still not ideal.
Procedural Cohesion: Functions are grouped because they are executed in a specific order. Example: A module with functions that perform steps in a particular process. Improves upon temporal.
Communicational Cohesion: Functions operate on the same data. Example: A module containing functions that process data from a single input file. Strong cohesion, good design.
Sequential Cohesion: Output of one function serves as input for another. Example: A module with functions where the output of one is the direct input of the next. Very strong cohesion.
Functional Cohesion: A module performs a single, well-defined function. Example: A module calculating the area of a circle. The strongest form of cohesion and ideal.