State Transition Diagram with example in software engineering

What is the State transition Diagram?

When we write our program in Object-oriented programming, then we need to take classes and objects. Objects change their states during different functions/actions performed on objects.

In a state transition diagram, the states appear as rounded rectangles with the state names inside.

Symbols used in State Transition Diagram 

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Terminologies of State Transition Diagram

State
In the state transition diagram, An object always remains in some state. Further, the state of the object may change after an event occur.

Event

Any activity that may trigger a state transition or can change the state.

Guard

In the state transition diagram, a guard is a boolean expression. Suppose if the guard is true, then it enables an event to trigger a transition.

Transition

The change of state within an object is represented with a transition. It is possible that an object changes its state when the transition occurs.

Action

One or more actions are taken by an object when the object changes a state.

Examples of State Transition Diagram

Case Study:

You need to develop a web-based application in such a way that users can search other users, and after getting search complete, the user can send the friend request to other users. If the request is accepted, then both users are added to the friend list of each other. If one user does not accept the friend request. The second user can send another friend request. The user can also block each other.

Solution:

1. First of all, identify the object that you will create during the development of classes in oop
2. Identify the actions or events
3. Identify the possible states for an object
4. Draw the diagram.

Object: friends 

Events or actions: Search to add a friend, add a friend, accept a friend, reject a friend, again add, block user and close.

States: Start, the friend added, friend rejected, user blocked and end.

Example: Draw the state transition diagram of the OS process

List of UML tools for drawing the diagrams

Here, we are showing you a list of UML tools for drawing the diagrams.

Advantages of State Transition Diagram

1. A state transition diagram is used to represent a finite state machine.
2. A state transition diagram is a demonstration of how our objects and functions behave within the system.

When I can Use State Transition Diagram?

1. When the system has some dependencies on the events or on the values in the past.
2. State Transition diagram can be used when a software tester is testing the system for a finite set of input values.
3. When the software tester focus is to understand the behavior of the object.
4. When the software tester focus is to test the sequence of events that may occur in the system under test.

Frequently Asked Questions (FAQ)

In a state transition diagram, the circle at the right with a hollow border is the initial state.

True/False

Answer: False

In a state transition diagram, the circle to the left is the final state.

True/False

Answer: False

Topic Covered

State Transition Diagram with example in software engineering.

State Transition Diagram MCQs

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