Modularity and three minor pillars of OOPs

Modularity: Modularity refers to breaking down software into different parts. A rigid object is broken into small pieces.

Modularity provides:

• re-usability
• parallel development of different modules making development faster
• module is easier to debug, update and modify.
• maintainability 

IS-A Relationship: It is like apple is a fruit. This has dependency ie. child class is dependent on parent class. It has tight coupling.

HAS-A Relationship: It is like apple has seeds. This is independent ie. child class has existence without parent class, eg. car has an engine where engine has existence without car.

Three minor pillars of OOPs: 

• Strong type-casting: Enforcement of th entity, such that objects of different types may not be interchanged, or at the most interchanged only in very restricted ways
• Persistence: Storing or saving the data for future use.
• Concurrency: Performing several tasks simultaneously or in parallel.