WEEK 9 UML State Transition Machines

Brunel University London Software Development and Management

Course Title: CS2002
Instructor: Dr. Rumyana Neykova
Contact: Rumyana.neykova@brunel.ac.uk

State Transition Machines

Diagram representation of states and transitions.
- occupy() Method: Changes the state to occupied.
- release() Method: Changes the state to free.

Literature Reference

Textbook: UML @ Classroom: An Introduction to Object-Oriented Modeling
- Authors: Martina Seidl, Marion Scholz, Christian Huemer, Gerti Kappel
- Publisher: Springer Publishing, 2015
- ISBN: 3319127411
Topics Covered:
- Use Case Diagram
- Structure Modeling
- State Machine Diagram
- Sequence Diagram
- Activity Diagram

Outline of Content

Introduction
States
Transitions
Types of Events
Types of States
Entry and Exit Points

UML Diagram Types

Structural Diagrams:
- Classes, Objects, Packages, Components
Behavioral Diagrams:
- State Machine, Use Case, Sequence, Activity Diagrams

Introduction to State Machine Diagrams

Definition: Models the states of a system or object.
Functionality:
- Shows possible states
- Illustrates state transitions via events
- Describes system behavior in each state
Example: Lecture hall object states.

Example: Lecture Hall Class

Class Structure:

class LectureHall {
    private boolean free;
    public void occupy() { free=false; }
    public void release() { free=true; }
}

Digital Clock Example

Clock Functionality:
- Methods: set(), inc()
- Entry Activities: beep on entry, show current time.

State Activities

Entry Activity: Action performed when entering a state.
Do Activity: Action performed during the state.
Exit Activity: Action performed when exiting the state.
Deferrable Trigger: Events that remain in the event pool if they do not trigger a transition.

State Definitions

States: Nodes representing active conditions of an object.
- Activity Types:
  - entry: Executed upon entering a state.
  - exit: Executed upon exiting a state.
  - do: Executed while active in the state.

Transitions

Definition: Change from one state to another.
Components:
- Source State
- Target State
- Event Trigger
- Guard Condition
- Activities Executed During Transition

Transition Syntax

Event (Trigger): Stimulus initiating a transition.
Guard (Condition): Boolean expression that must be true to proceed with the transition.
Activity (Effect): Actions performed as a result of the transition.

Transition Types

Internal Transition: Remains in current state while executing actions.
External Transition: Leaves current state to enter a different state while executing actions.

Sequence of Activity Executions

Scenario: Evaluating variable 'x' during transitions between states.

Example: Registration Status

States: Not registered, registered.
Transitions: Registration potential, withdrawal options.

Event Types

Signal Event: Triggered by receiving a signal.
Call Event: Triggered by operation calls.
Time Event: Based on relative or absolute timing.

Change Event vs. Guard

Change Event: Checked continuously for condition changes.
Guard: Checked only when an event occurs.

Initial State

Definition: Starting point in a state machine; cannot stay in this state.

Final State and Terminate Node

Final State: Represents the logical end of the state's sequence.
Terminate Node: Ends the state machine and ceases object existence.

Decision Node

Functionality: Models alternative transitions based on conditions.

Parallelization and Synchronization Node

Parallelization Node: Splits control flow into multiple paths.
Synchronization Node: Merges multiple flows back into one.

Summary of State Machine Elements

State: Defined period of object life during which activities can occur.
Transition: Movement from one state to another.
Initial State: Start of the state machine.
Final State: Conclusion of the state machine.
Terminate Node: Marks the end of the object's lifecycle.