CS251 – Software Engineering Lectures 11 State Diagrams Read Reading 8 Chapter 8 (only 8.2) from OO SE 2/e, Slides by: Timothy Lethbridge

Chapter 5: Modelling with classes Last Lecture Where are we now ? why Modeling software ? Sequence diagram ? Chapter 5: Modelling with classes © Lethbridge/Laganière 2012

Chapter 5: Modelling with classes Outline State diagrams Modelling states and transitions Modelling activities and actions Examples Chapter 5: Modelling with classes © Lethbridge/Laganière 2012

Chapter 8: Modelling Interactions and Behaviour 8.2 State Diagrams A state diagram describes the behavior of a system, some part of a system, or an individual object. At any given point in time, the system or object is in a certain state. Being in a state means that it is will behave in a specific way in response to any events that occur. Some events will cause the system to change state. In the new state, the system will behave in a different way to events. A state diagram is a directed graph where the nodes are states and the arcs are transitions. Chapter 8: Modelling Interactions and Behaviour © Lethbridge/Laganière 2005

State diagrams – an example tic-tac-toe game Chapter 8: Modelling Interactions and Behaviour © Lethbridge/Laganière 2005

State diagrams – an example Chapter 8: Modelling Interactions and Behaviour © Lethbridge/Laganière 2005

Chapter 8: Modelling Interactions and Behaviour States At any given point in time, the system is in one state. A state is represented by a set of values for the attributes of the given object. It will remain in this state until an event occurs that causes it to change state. Chapter 8: Modelling Interactions and Behaviour © Lethbridge/Laganière 2005

Chapter 8: Modelling Interactions and Behaviour States A state is represented by a rounded rectangle containing the name of the state. Special states: A black circle represents the start state A circle with a ring around it represents an end state Chapter 8: Modelling Interactions and Behaviour © Lethbridge/Laganière 2005

Chapter 8: Modelling Interactions and Behaviour State Diagram States Transitions Events Activities Actions Initial state event transition state off hook Idle Active on hook Chapter 8: Modelling Interactions and Behaviour © Lethbridge/Laganière 2005

Chapter 8: Modelling Interactions and Behaviour Transitions A transition represents a change of state in response to an event. The label on each transition is the event that causes the change of state. Chapter 8: Modelling Interactions and Behaviour © Lethbridge/Laganière 2005

Example dial tone dialling idle digit (n) on-hook off-hook on-hook State Event Transition digit (n) digit (n) dial tone dialling on-hook off-hook on-hook idle

State diagrams – an example with conditional transitions action condition

State diagrams – an example with conditional transitions Add these info to the last state diagram (a) The course section can be canceled when in any state, except after it has been taught. (b) A student can drop out at any time, except after the course section has been taught.

Activities in state diagrams An activity is something that takes place while the system is in a state. It takes a period of time. The system may take a transition out of the state in response to completion of the activity, Some other outgoing transition may result in: The interruption of the activity, and An early exit from the state. Chapter 8: Modelling Interactions and Behaviour © Lethbridge/Laganière 2005

State diagram – an example with activity Audio Playing Chapter 8: Modelling Interactions and Behaviour © Lethbridge/Laganière 2005

Chapter 8: Modelling Interactions and Behaviour Types of Events External Event (also known as system event) is caused by something outside the system boundary e.g. when a cashier presses the “enter item” button on a POST, an external event has occurred. Internal Event is caused by something inside our system boundary. In internal event arises when an operation is invoked via a message sent from another internal object. Temporal Event is caused by the occurrence of a specific date and time or passage of time. Chapter 8: Modelling Interactions and Behaviour © Lethbridge/Laganière 2005

Actions in state diagrams An action is something that takes place effectively instantaneously When a particular transition is taken, Upon entry into a particular state, or Upon exit from a particular state An action should consume no noticeable amount of time Chapter 8: Modelling Interactions and Behaviour © Lethbridge/Laganière 2005

State diagram – an example with actions Chapter 8: Modelling Interactions and Behaviour © Lethbridge/Laganière 2005

Nested substates and guard conditions A state diagram can be nested inside a state. The states of the inner diagram are called substates. Chapter 8: Modelling Interactions and Behaviour © Lethbridge/Laganière 2005

State diagram – an example with substates Chapter 8: Modelling Interactions and Behaviour © Lethbridge/Laganière 2005

Chapter 8: Modelling Interactions and Behaviour © Lethbridge/Laganière 2005

Example: Online Chess

ExampleOnline Chess

ESE — Modeling Behaviour Example: Phone ESE — Modeling Behaviour © Oscar Nierstrasz

Chapter 5: Modelling with classes Outline State diagrams Modelling states and transitions Modelling activities and actions Examples Chapter 5: Modelling with classes © Lethbridge/Laganière 2012

Chapter 5: Modelling with classes Readings and Videos Very Important R8: Chapter 8 (Modeling interactions and behavior) of OOSE, 2nd ed by Timothy Lethbridge Read section 8.2 from page 291 to page 301 Appendix A: Summary of UML Syntax – page 471 and 472 http://agilemodeling.com/artifacts/stateMachineDi agram.htm Chapter 5: Modelling with classes © Lethbridge/Laganière 2012