How to Draw State Transition Diagram in Uml TUTORIAL

This postal service was originally published on June 12, 2019, and updated almost recently on September xiv, 2020.

State diagrams are one of those things that seem intimidating at start, only once you beginning using them, y'all'll wonder how y'all e'er did without. Merely earlier we go into the diagramming part, first we demand to sympathise what a land car is.

A state machine is a device that stores the status of an object at whatsoever given fourth dimension. Information technology tin simulate sequential logic, too as model issues in various fields, including AI, maths, linguistics, and game development. A state machine can also change the object's status or crusade other actions based on its input.

If yous want to sympathise all the possible states and show how an object gets to and from each state, you'll want to visualize it. Hence, the country diagram.

What is a state diagram?

A land diagram is a graphic representation of a state machine. It shows a behavioral model consisting of states, transitions, and deportment, also as the events that affect these. It'due south also ane of the 14 Unified Modeling Languages (UML) used for specifying, visualizing, constructing, and documenting software systems.

State machine diagram template available in Cacoo

What's the difference between a state diagram and a flowchart? Well, despite having a conspicuously defined start and end bespeak, state diagrams aren't useful for showing a progression of events because they describe transitions. So they're meliorate for showing shifts in beliefs.

A flowchart shows the processes that change the state of an object. A state diagram shows the actual changes in state, not the processes or commands that created those alter.

How tin can a state diagram aid you?

It's useful for showing the progress of event-driven objects in a reactive system, such equally an ATM. Starting time, the automobile is either on or out of order. When the carte du jour'due south inserted, the user enters their pin. If it'due south right, they're taken to another set of options. If incorrect, the process is ended.

State diagrams are also useful for describing how an object moves through various states within its lifetime. For instance, the motility of an bookish through their career: they begin every bit a freshman, then move to sophomore, junior, and and then senior.

How to depict a country diagram

Each diagram usually begins with a dark circumvolve that represents the initial state and ends with a bordered circle that represents the terminal country. States are denoted with rectangles with rounded corners. Each rectangle is labeled with the proper noun of the state. And transitions are marked with arrows that link one state to some other, showing how the states modify. You'll notice a run through of the near popular symbols below.

Composite country (also known as a 'nested state')

This refers to a state that encompasses various sub-states, which are nested into information technology. Sub-states are used to simplify complex flat state diagrams by showing that some states are simply possible within a particular context. In the air toaster oven example below, the 'heating' status of the machine represents the blended/nested land.

Toaster oven land automobile with entry and exit deportment

Selection pseudostate

This is represented past a diamond shape on the diagram. It indicates a dynamic status that has several potential results.

An extended state auto of "inexpensive keyboard" with extended state variable key_count and various baby-sit atmospheric condition

Trigger

This is a message that moves an object from state to state. In the keyboard example below, pressing CapsLock is the triggering event. If the keyboard is in the "default" state, pressing CapsLock will crusade the keyboard to enter the "caps_locked" land. However, if the keyboard is in the "caps_locked" state, pressing CapsLock will cause the keyboard to enter the "default" land.

UML state diagram representing the computer keyboard state machine

Event or Transition

This is when a moment triggers a shift. These are represented by labeled transition arrows. In the case in a higher place, pressing CapsLock is the outcome that triggers the 'default' and 'caps_locked' states.
→

Initial State

This represents the first state in the procedure. It appears as a dark circumvolve with an arrow leading from it.

⚫→

Concluding State (or terminator state)

This represents the object'southward final state. Information technology appears as an arrow pointing to a filled circle nested within another circumvolve.

←
Exit point

A circumvolve with an Ten through it represents the point at which an object escapes the country machine. The get out indicate is used when the process is interrupted or left incomplete due to an error or event.

Guard

This is a boolean condition that must be true for a land transition to occur. If the condition is false, the transition does not occur. It'south written higher up the transition pointer.

State

States represent the current status of an object and appear as a rounded rectangle. In the example below, 'Closed', 'Open', and 'Deleted' are all states.

Country transition diagrams

This refers to when the object transitions from one state to another, the events that must have taken place before the transition can occur, and the activities during the life of the object.

Substate

This refers to a land contained within a blended state'due south region. In the toaster oven case above, 'toasting' and 'baking' are sub-states in the larger 'heating' composite land.

State diagram examples

Source: uml-diagrams.org

Source: lucidchart.com

Final thoughts

State diagrams are an essential tool for visualizing system behavior. Setting this information out in a diagram means yous can encounter an object's behavior throughout its entire lifespan, as well as the unlike events that crusade diverse transitions, at a glance.

Pick out your defended diagramming software — ideally one that has a robust library of UML templates and shapes — and begin making your first state diagram today. If you're working with a squad, make sure you invest in software that lets you work collaboratively with your squad in real-time, so you can edit diagrams together, hands share with others, and go feedback right on your sheet.

Interact on ideas to align your squad's vision in Cacoo

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Georgina Guthrie Georgina is a displaced Brit currently working in France as a freelance copywriter. Before moving to sunnier climates, she worked equally a B2B bureau writer in Bristol, England, which is also where she was born. In her spare time, she enjoys old films and cooking (badly).

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How to Draw State Transition Diagram in Uml TUTORIAL

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