SD

State Diagram
Determines the state of objects of an application
For only objects of those classes who have important temporal behaviour

Syntax

Shape	Purpose
Rounded Rectangle	Contains State Name
Arrow Lines	Connection btw states
Rectangle	Boundary
Pentagonal tag	Represents Class Name
Brackets	Guard Statement
Filled Dot	Entry Point
Encircled Filled Dot	Exit Point
event/{ description }	activities within state
Vertical line - another diagram	Concurrent states

Syntactical Rules

• State names are adverb (very common to end with ing)
• Events cause transition from one state to another
• Event names are written on top of the arrow lines (lower camel case italics)
• There can be multiple exit points, like on multiple signal triggers
• Unlabelled transition is a completion transition (from end to start)
• Activities can be performed within the states such as enter, do, exit.
  • We can define common and constant tasks in these activities

Info

• States represent Intervals of time
• Events represent Point in Time

Types of Events

Following are the types of events:

Signal Events

• Purpose : Change state
• Can be Guarded
  • Only change the state on that external signal if condition is satisfied
  • Example would be to change state to FULL when currentSeats >= maxSeats
  • The guard statement will be in Regular Font but signal name will be italics.

Change Events

• keyword : when (…)

Time Events

• Absolute
  • keyword : when (…)
• Relative
  • keyword : after (…)

Types of SD

Following are the types of State Diagrams:

One-Shot

• Distinct time for object to be created and destroyed (start and end)

Continuous

• No start or end (continuous existence)

Nested States

State diagram within state diagram
Can be used used to demonstrate sub abstract state within a state diagram
It needs to have its explicit entry point if no arrow points to one of its state
Convention: Rounded Rectangle same as a state

State Machine

Further elaborates a state
Can be used to define activities and sub states within a state
Convention: {StateName} : {MachineName}

Concurrent States

Determine states that are triggered at the same time
For Concurrent tasks
Convention: {Vertical line connecting each state within a circular rectangle boundary}
Each concurrent task should be separated by a horizontal dashed line