Explain different types of cohesion and coupling in system design

Cohesion and coupling are two key characteristics that are used to evaluate the efficiency of a program structure in terms of its manageability, understandability, and changeability.

Cohesion refers to the degree to which the elements of a module belong together. In other words, it measures the strength of relationship between the module's responsibilities. There are seven types of cohesion, listed from worst to best:

1. Coincidental Cohesion: Elements within a module have no significant relationship.
2. Logical Cohesion: Elements perform similar activities, selected from outside module.
3. Temporal Cohesion: Elements are related in time and are executed together.
4. Procedural Cohesion: Elements contribute to a common activity.
5. Communication Cohesion: Elements contribute to a common activity and share information.
6. Sequential Cohesion: Output from one part of a module serves as input to another part.
7. Functional Cohesion: All elements contribute to a single, well-defined task.

Coupling, on the other hand, refers to the degree of interdependence between modules. It measures how closely the modules in a system or a program are linked or connected to each other. There are five types of coupling, listed from best to worst:

1. Data Coupling: Modules share data through, for example, parameters.
2. Stamp Coupling: Data structure shared between modules.
3. Control Coupling: One module controlling the flow of another.
4. Common Coupling: Two modules share the same global data.
5. Content Coupling: One module uses the content of another module.

In system design, the goal is to maximize cohesion and minimize coupling. High cohesion within modules and low coupling between modules leads to high readability and maintainability, and makes the system more flexible, modular, and predictable.