UML Syntax Guide

UML (Unified Modeling Language) is a standard used to create software blueprints.

There are two main types of UML diagrams:
- Structure diagrams: show the static structure of a system, its components at different levels of abstraction and implementation, and how they are related to each other.
- Behavior diagrams describe the dynamic behavior of a system, representing how objects interact and how the system changes over time.

1. Component Diagrams

Component Diagram describes the static implementation view of a system.
It shows components, their interfaces, and relationships.
It is used in Component-Based Development (CBD) and SOA.
Components are reusable, replaceable, and independently deployable.
Use this when:
- Designing system architecture
- Breaking system into modules/components
- Showing how components interact
- …

Class Diagram is UML structure diagram which shows structures of the designed system at the level of classes and interfaces, shows their features, constraints and relationship (associations, generalizations, dependencies,..)
Use this when:
- Designing classes and their structure,include attributes and methods before coding
- Showing relationships between classes
- Detailing components at a deeper level
- …

Abstract Class: The name of an abstract class, method is shown in italics. An abstract classifier can also be shown using the keyword {abstract} or <<abstract>> after or below the name.
Static: Class (i.e. static) methods and fields are indicated by underlining
Constant: (i.e. final) fields are indicated via naming convention: constants should be in ALL_CAPS

State machine diagram is a behavior diagram which shows discrete behavior of a part of designed system through finite state transitions. State machine diagrams can also be used to express the usage protocol of part of a system.
Use this when object behavior changes based on state.

Activity Diagram is a UML behavior diagram that shows the flow of control or object flow, focusing on sequence and conditions.
Actions can be triggered by completion of other actions, availability of data, or external events.
Use this when:
- Modeling workflow or business processes
- Describing step-by-step logic (like algorithms)
- Showing conditions, loops, and parallel flows
- Explaining how different parts of a system interact over time
Example: Library System – Borrow Book Flow
- User searches for a book
- System checks availability
  - If available -> proceed to borrow
  - If not -> show unavailable message
- User confirms borrow
- System creates loan record
- Book status updated to “Borrowed”

Sequence Diagram is an interaction diagram that shows how objects communicate through messages over time.
It focuses on the order of messages between lifelines.
Use this when:
- Modeling interactions between components or objects
- Showing step-by-step message flow for a use case
- Designing APIs or method calls between classes
- …

Activity Diagram
- Purpose: model workflows
- Example: Borrow Book process
  - Search book -> Check availability
  - If available -> Borrow
  - Else -> Show unavailable
  - …

Component Diagram
- Purpose: define system structure
- Example components:
  - User Interface
  - Book Management
  - User Management
  - Borrow/Return Service
  - Database

Class Diagram
- Purpose: design internal structure of components
- Example:
  - Book (title, author, status)
  - User (userId, name)
  - Loan (borrowDate, returnDate)
  - BorrowService (borrowBook(), returnBook())
Sequence Diagram
- Purpose: show interaction between objects
- Example: Borrow Book
- User -> UI: request borrow book
  - UI -> BorrowService: borrowBook()
  - BorrowService -> Book: checkAvailability()
  - BorrowService -> Loan: createLoan()
  - BorrowService -> Book: updateStatus(“Borrowed”)
  - UI -> User: confirm success
State Machine Diagram
- Purpose: model object states
- Example: Book states
  - Available -> Borrowed -> Returned