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

1. Introduction

2. States

3. Transitions

4. Types of Events

5. Types of States

6. 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

1. State: Defined period of object life during which activities can occur.

2. Transition: Movement from one state to another.

3. Initial State: Start of the state machine.

4. Final State: Conclusion of the state machine.

5. Terminate Node: Marks the end of the object's lifecycle.