It appears as a dark circle with an arrow leading from it. The initial state represents the first state in the process. In the example above, pressing CapsLock is the event that triggers the ‘default’ and ‘caps_locked’ states. Labeled transition arrows represent events. UML state diagram representing the computer keyboard state machine Event or TransitionĮvents occur when a moment triggers a shift. However, if the keyboard is in the “caps_locked” state, pressing CapsLock will cause the keyboard to enter the “default” state. If the keyboard is in the “default” state, pressing CapsLock will cause the keyboard to enter the “caps_locked” state. In the keyboard example below, pressing CapsLock is the triggering event. An extended state machine of “cheap keyboard” with extended state variable key_count and various guard conditions TriggerĪ trigger is a message that moves an object from state to state. It indicates a dynamic condition that has several potential results. Toaster oven state machine with entry and exit actions Choice pseudostateĪ diamond shape on the diagram represents the choice pseudostate. In the air toaster oven example below, the ‘heating’ status of the machine represents the composite/nested state. Sub-states are used to simplify complex flat state diagrams by showing that some states are only possible within a particular context. Composite state (also known as a ‘nested state’)Ī composite or nested state refers to a state that encompasses various sub-states, which are nested into it. You’ll find a run-through of the most popular symbols below. Transitions are marked with arrows that link one state to another, showing how the states change. Rectangles with rounded corners denote a state, and each one includes a label with the name of the state. How to draw a state diagramĮach diagram usually begins with a dark circle that represents the initial state and ends with a bordered circle that represents the final state. For example, the movement of an academic through their career: they begin as a freshman, and then move on to sophomore, junior, and senior levels. State diagrams are also useful for describing how an object moves through various states within its lifetime. If it’s correct, the machine shows the next set of options. Then, the user inserts their card and enters a PIN. First, the machine is either on or out of order. How can a state diagram help you?Ī state diagram is useful for showing the progress of event-driven objects in a reactive system, such as an ATM. A state diagram shows the actual changes in state, not the processes or commands that created those changes. They depict transitions, so state diagrams are better for showing shifts in behavior.Ī flowchart shows the processes that change the state of an object. Well, despite having clearly defined start and end-points, state diagrams aren’t useful for showing a progression of events. State machine diagram template available in Cacoo What’s the difference between a state diagram and a flowchart? If you haven’t already guessed, a state diagram is one type of behavioral diagram. Structural UML diagrams depict the static framework of a system or process, while behavioral UML diagrams show the dynamic changes within a system. UML diagrams consist of two groups: structural and behavioral. It’s also one of the 14 Unified Modeling Languages (UML) used for specifying, visualizing, constructing, and documenting software systems. It shows a behavioral model consisting of states, transitions, and actions, as well as the events that affect these. What is a state diagram?Ī state diagram is a graphic representation of a state machine. If you want to understand all the possible states and show how an object gets to and from each state, you’ll want to visualize it. A state machine can also change the object’s status or cause other actions based on its input. It can simulate sequential logic, as well as model problems in various fields, including AI, maths, linguistics, and game development. But before we get into the diagramming part, first we need to understand what a state machine is.Ī state machine is a device that stores the status of an object at any given time. A state diagram is one of those things that seems intimidating at first, but once you start using it, you’ll wonder how you ever did without.
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