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Week 6: Object-Oriented Design - MCQ Focus

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🔹 1. Core Principles in OOD

Cohesion and Coupling

Cohesion: How closely related the responsibilities of a class or module are. High cohesion is preferred, meaning each module or class has a clear, single responsibility.

Coupling: Degree of dependency between classes or modules. Low coupling is ideal to ensure independence and flexibility in the system.

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🔹 2. OOD Key Concepts

Abstraction

Definition: Simplifies complexity by focusing on essential features, hiding implementation details.

Example: A Shape class hides specific details of shapes like Circle and Rectangle and exposes only general features like Draw().

Encapsulation

Definition: Restricts direct access to some of an object's components, bundling data with methods to protect it.

Usage: Commonly achieved in C# through private fields and public properties.

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🔹 3. Identifying Classes and Methods in OOD

Classes: Typically represent nouns in problem descriptions (e.g., Student, Course).

Methods: Often correspond to verbs, representing actions or behaviors (e.g., Enroll, UpdateStatus).

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🔹 4. User Stories and Their Role in OOD

Structure of a User Story

Format: “As a [user type], I want to [perform action] so that [achieve benefit].”

Purpose: Helps in understanding user needs and prioritizing features.

Components:

Persona: User type (e.g., “Unit Coordinator”)

Action: Specific task (e.g., “Create a unit with a code, name, and student count”)

Benefit: Value achieved by completing the task

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🔹 5. Software Development Models

Waterfall Model

Sequential Process: Stages include Requirements → Design → Implementation → Testing.

Ideal for: Projects with clear, unchanging requirements.

Downside: Difficult to go back and make changes after a stage is completed.

Iterative and Incremental Model

Process: Develops the system through repeated cycles (iterations) and adds functionality in small chunks (increments).

Ideal for: Projects where requirements evolve or need refinement over time.

Benefit: Allows for continuous testing and adaptation.

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🔹 6. UML Class Diagrams - Focus on Relationships

Purpose: Graphically represents classes, attributes, methods, and relationships.

Common Relationships in Class Diagrams

Association (uses-a): Two classes collaborate without a strong dependency (e.g., Teacher uses Student in Teach(Student student)).

Aggregation (has-a): An object contains another, but they can exist independently (e.g., Library has Books).

Composition (part-of): A strong ownership where the lifecycle of the contained object depends on the containing object (e.g., Car has Engine, and when Car is destroyed, so is Engine).

Inheritance (is-a): A derived class shares attributes and behaviors from a base class (e.g., Employee is a Person).

UML Notations:

Visibility:

+ Public

- Private

# Protected

Arrows for Inheritance: Solid line with an empty arrowhead.

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✨ Quick MCQ Tips

Focus on Definitions: Know what each OOD concept (abstraction, encapsulation, cohesion, coupling) means.

Class Relationships: Be able to identify and distinguish between composition, aggregation, association, and inheritance.

Understand User Stories: Recognize the structure and purpose, especially how they help clarify user needs and prioritize features.

Model Differences: Be clear on differences between Waterfall (sequential) and Iterative (incremental, adaptable).

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