State Machines - Software Engineering - Lecture Notes, Study notes of Software Engineering

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State Machines &

Advanced State Machines

Outline

 State machines:

 Introduction

 State machine diagrams

 States

 Transitions

 Events

 Advanced state machines:

 Composite states

 Simple  Orthogonal

 Submachine states

 Submachine communication

 History

Introduction

 Reactive objects:

 Respond to external events

 May generate and respond to internal events

 Have a lifecycle modeled as a progression of

states, transitions and events

 May have current behavior that depends on past

behavior

 State machines are used to model behavior

of classifiers such as classes, use cases,

subsystems, systems

Introduction

 There are two types of state machines:

 Behavioral state machines

 Protocol state machines

 State machines are most commonly used to model

dynamic behavior of classes

 In UP, state machines can be used in: requirements,

analysis, design

 A significant challenge is testing state machines:

manual walkthrough, simulation, code generation +

test harnesses for state machines

States

Summary of UML state syntax, Fig.21.4 [Arlow & Neustadt 2005]

Transitions

Summary of UML syntax for transitions in behavioral state diagrams, Fig.21.5 [Arlow & Neustadt 2005] Where:  event(s)= internal or external occurrence(s) that trigger the transition  guardCondition = boolean expression, when true the transition is allowed  anAction = some operation that takes place when the transition fires

Transitions

A junction pseudo-state represents a point where transitions merge or

branch, e.g. Fig.21.7 [Arlow & Neustadt 2005]

Transitions

A junction pseudo-state may have more than one output transition

(protected by mutually exclusive guard conditions) e.g. Fig.21. [Arlow & Neustadt 2005]

Events

 Events can be of four types:

 Call event

 Signal event

 Change event

 Time event

Events

Example of a call event, Fig.21.11 [Arlow & Neustadt 2005]

Events

Change events are positive edge triggered. Example of a change event, Fig. 21.15 [Arlow & Neustadt 2005]

Events

Time events are indicated by the keywords when and after.

Example of a time event, Fig. 21.16 [Arlow & Neustadt, 2002]

Composite states

 A composite state

contains one or more nested state machines

( submachines), each

existing in its own

region, Fig 22.2 [Arlow

& Neustadt 2005].  The composition icon is shown in Fig. 22.

Simple composite states

 A superstate that contains a single region is called a simple

composite state, e.g. Fig 22.5 [Arlow & Neustadt 2005]