Solution

Cohesion

Definition: Measure of functional relatedness within a module. High cohesion is desired (elements belong together).

Types (best → worst):

1. Functional - single function (e.g., compute salary) - BEST
2. Sequential - output of one element is input to next
3. Communicational - operates on same data
4. Procedural - related by procedure sequence
5. Temporal - related by time (initialization)
6. Logical - logically related (e.g., all inputs)
7. Coincidental - arbitrary grouping - WORST

Coupling

Definition: Measure of interdependence between modules. Low coupling desired.

Types (best → worst):

1. Data - via parameters - BEST
2. Stamp - via data structure
3. Control - via control flag
4. External - via external format
5. Common - via global data
6. Content - one modifies other - WORST

Usefulness in Good Design

• High cohesion + Low coupling → Modules independent, reusable, testable, maintainable. Change in one does not ripple.
• Reduces error propagation, improves understandability and modifiability (as Q33 explains: limited modification, reusable, reduced propagation → all of above).

Principle: Maximize cohesion, Minimize coupling.