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Lecture on UML Static and Object Interaction Diagrams

Learning Outcomes:

Unified Modeling Language (UML)

- the two primary diagrams: **static** (Class diagrams) and **object interaction** (Sequence diagrams).

- These tools are essential for visualizing, specifying, constructing, and documenting the artifacts of software systems.

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## 1. Static (Class) Diagrams

### 1.1 Introduction - Class diagrams are the most common diagrams used in UML. - They show the static structure of the system, emphasizing classes, attributes, operations, and relationships.

### 1.2 Components of a Class Diagram 1. **Class**: Represented by a rectangle, divided into three parts: - Class name - Attributes - Operations (methods) 2. **Relationships**: Represented using different types of lines. - **Association**: A plain line. - **Aggregation**: A diamond line pointing to the whole. - **Composition**: A filled diamond line pointing to the whole. - **Inheritance**: A line with a triangle arrow pointing to the base class. ### 1.3 Exercise: Sketch a Class Diagram

**Scenario**: Model a simple library system.

1. **Book**: - Attributes: title, author, ISBN. - Operations: checkout(), returnBook(). 2. **Member**: - Attributes: name, memberID. - Operations: borrowBook(), returnBook(). 3. A **Member** can borrow multiple **Books**, but a **Book** can be borrowed by one **Member** at a time.

**Task**: Draw the class diagram based on the above description.

> [Expect students to draft a sketch. Discuss different versions and fine-tune the class relationships.]

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## 2. Object Interaction (Sequence) Diagrams

### 2.1 Introduction - Sequence diagrams display the dynamic interactions between objects. - They emphasize the sequence of messages exchanged between objects over time.

### 2.2 Components of a Sequence Diagram 1. **Object**: Represented by a rectangle at the top. 2. **Activation Bar**: Thin rectangles that show an object's period of activity. 3. **Messages**: Horizontal arrows representing communication between objects. 4. **Return Message**: Dashed horizontal arrows indicating the return of a message. 5. **Lifeline**: Dashed vertical line representing the object's existence.

### 2.3 Exercise: Sketch a Sequence Diagram

**Scenario**: Depict how a `Member` borrows a `Book` from a `Library`.

1. The `Member` requests a `Book`. 2. The `Library` checks if the `Book` is available. 3. If available, the `Library` processes the borrowing. 4. The `Book` is marked as borrowed, and the `Library` sends a confirmation to the `Member`.

**Task**: Draw the sequence diagram based on the above interactions.

> [Expect students to draft a sketch. Discuss different sequence representations and the order of messages.]

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## Closing Thoughts

UML diagrams are powerful tools to represent complex systems. Mastering them will help you design, communicate, and understand software projects more effectively.

For your homework, please model a new system of your choice using both a static class diagram and an object interaction sequence diagram.

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