Below is a UML Class Diagram for an Online Banking System, with necessary assumptions clearly stated.

Assumptions:

1. A customer can have multiple bank accounts.
2. Each account belongs to one customer.
3. Customers access the system using login credentials.
4. Transactions can be Deposit, Withdrawal, or Transfer.
5. An admin manages customers and accounts.

Question 1 of MCS-219: Object Oriented Analysis and Design.
Answer: OOAD (Object-Oriented Analysis and Design) is a software engineering approach that focuses on modeling a system as a collection of interacting objects. These objects represent real-world entities and combine data (attributes) with behavior (methods).
OOAD helps in understanding system requirements (analysis) and translating them into a robust, reusable, and maintainable software design (design).