To avoid such unfavorable scenarios, we prepare the knowledge base. In the glossary we gather the main specialized terms that are frequently used in the working process. All meanings are written according to their generally accepted international interpretation. For convenience, you can use the search bar to simplify and speed up the search process. History states allow the state machine to re-enter the last sub-state that was active prior to leaving the composite state.

definition of state diagram

A state diagram is a diagram used in computer science to describe the behavior of a system considering all the possible states of an object when an event occurs. This behavior is represented and analyzed in a series of events that occur in one or more possible states. Each diagram represents objects and tracks the various states of these objects throughout the system. In nature; however, a flowchart shows the processes within a system that alters the state of an object rather than the actual state changes themselves.

For mealy model, the directed line is labeled with binary numbers separated with ‘/’, as shown in the below diagram. In this diagram, each present state is represented inside a circle. S1 and S2 are states and S1 is an accepting state or a final state. This example shows an acceptor for strings over that contain an even number of zeros. A state is a constraint or a situation in the life cycle of an object, in which a constraint holds, the object executes an activity or waits for an event.

state diagram (state machine diagram or statechart diagram)

This is also a pseudo-state because it does not have any variable or action described. This example shows an acceptor for binary numbers that contain an even number of zeros. Activity diagram explained in the next chapter, is a special kind of a Statechart diagram. As Statechart diagram defines the states, it is used to model the lifetime of an object.

There are other sets of semantics available to represent state diagrams. For example, there are tools for modeling and designing logic for embedded controllers. These diagrams, like Harel’s original state machines, support hierarchically nested states, orthogonal regions, state actions, and transition actions. Are often used to represent the dynamic behavior of systems. The state diagram thus defines a set of possible sequences of events and states.

definition of state diagram

They are used to model and construct the functionality of a system. So, a behavior diagram simply guides us through the functionality of the system using definition of state diagram Use case diagrams, Interaction diagrams, Activity diagrams and State diagrams. Activity is an ongoing non-atomic execution within a state machine.

Get Visual Paradigm Community Edition, a free UML software, and create your own State Machine Diagram with the free State Machine Diagram tool. StudySmarter is commited to creating, free, high quality explainations, opening education to all. By registering you get free access to our website and app which will help you to super-charge your learning process. A change of state is caused by a change in temperature or a change in pressure.

Combined Science

A state diagram is a dynamic model that shows the state changes that an object goes through during its lifetime in response to events. It is used to help the developer better understand any complex functionality of specialized areas of the system. A state diagram is also called as state chart diagrams, depict the dynamic behavior of the system in response to external and internal events. A state machine generally has no notion of such a progression. A state in a state machine is an efficient way of specifying a particular behavior, rather than a stage of processing.

  • In general, the temperature and pressure of the material would have to be very low for this to occur.
  • A state diagram is used to represent the condition of the system or part of the system at finite instances of time.
  • Lastly, all of the events that trigger state changes are labeled as transition elements.
  • For example, there are tools for modeling and designing logic for embedded controllers.
  • This increases the common understanding of the participants about the modelled object.
  • The first state is an idle state from where the process starts.
  • Transitions connect two states, i.e. a source node and a destination node.

The elements that constitute a state diagram are rounded boxes representing the states and arrows showing transitions to the next state. The activity section depicts the activities the object performs while it is in that state. Every state diagram starts with an initial state, which is the state where the object is created. Right after the initial state, objects change their states, and the next state is determined by conditions based on activities.

This makes the behavior of the object visible and comprehensible. A system that can be modeled with a state diagram could be an ATM. The initial state of the system is “ready” to be triggered into action by a customer. Middle states could include verifying the user, processing the request or malfunctioning. Events are determined by the user, such as checking bank balance, withdrawing cash or depositing a check.

Frequently Asked Questions about Changes of state

A guard condition is evaluated after the trigger event for the transition occurs. It is possible to have multiple transitions from the same source state and with the same event trigger, as long as the guard conditions don’t overlap. A guard condition is evaluated just once for the transition at the time the event occurs. The boolean expression may reference the state of the object.

definition of state diagram

Enter this state, it might be desirable to return to the main sequence of states as soon as possible. This can be achieved by returning S3 to S0 via a transition which is initiated by the first clock pulse that occurs after the entry into S3. On the other side, there are a lot of SDL constructs that cannot be expressed in UML. For example the body of a newtype declaration, signal lists, connection of multiple channels, timers in general and priority. But there is one SDL feature that is particularly difficult to translate, namely the join. The join, together with the decision, allows one transition to have different paths and merge after some actions.

Environmental Science

Classic state diagrams require the creation of distinct nodes for every valid combination of parameters that define the state. This can lead to a very large number of nodes and transitions between nodes for all but the simplest of systems . This complexity reduces the readability of the state diagram. With Harel statecharts it is possible to model multiple cross-functional state diagrams within the statechart. Each of these cross-functional state machines can transition internally without affecting the other state machines in the statechart. The current state of each cross-functional state machine in the statechart defines the state of the system.

Unless there is an abnormal exit , the exit from the composite state occurs when both substates have exited. A nested state machine may have at most one initial state and one final state. Substates are used to simplify complex flat state machines by showing that some states are only possible within a particular context . State represent the conditions of objects at certain points in time.

In State Machines the vertices represent states of an object in a class and edges represent occurrences of events. The additional notations capture how activities are coordinated. The state of an object depends on its current activity or condition. A State Machine Diagrams shows the possible states of the object and the transitions that cause a change in state.

They help to describe system behavior and to define requirements. Due to their logical structure with specified states, transitions, events and conditions, they are ideally suited for modeling workflows using software. Visualisation of the various elements in the form of state diagrams is usually superior to documentation with tables. Nevertheless, companies must decide for which objects they want to use state diagrams to describe. Just because state diagrams provide an easy way to display, does not mean that organisations should now only sketch corresponding diagrams. It is advisable to use state diagrams only for complex objects, because the added value of using state diagrams is rather low for simply structured objects.

In addition, there is also a behavior that is executed when an event occurs, e.g. a “peep” noise during a mouse over. In addition to such signal events, there are call events for the reception of messages, time events for state transitions over time or at defined times and change events. In the case of a change event, a condition is permanently checked and a corresponding change of state is triggered if no monitoring condition blocks this. In contrast, a condition is only checked if an assigned event occurs. Inner transitions are the reactions to an event that triggers an activity but not a state transition. No entry or exit activities are performed due to the missing state change .

definition of state diagram

We use it to state the events responsible for change in state . Let’s refine the state machine example above to prevent burning out the bread, heater of the toaster must produce heat in temperature interval . Graphically, a state is rendered as a rectangle with rounded corners. The lifecycle of an object, from initialisation to release, can be modelled.

Speak with the team in the same language

The behavior diagrams should always be designed in such a way that they can be read easily from top left to bottom right. Although a state diagram should describe the entire behavior of a state machine, it can be very useful to refine details in subordinate diagrams. Basically, however, the UML 2.5 notation or its equivalent in SysML offers a clear and understandable structure that is easy to create and understand. The permitted states of an object and the events triggered by state transitions can be described.

It is nothing but the input value which causes the transition. The input value, which causes the transition to occur is labeled first ‘1/’. The output produced for the corresponding input is labeled second ‘/0’.

Basic components of a statechart diagram –

An action is an operation that is invoked by an entity that is modeled. A very traditional form of state diagram for a finite machine is a directed graph. There exist different types of state diagrams that have different semantics and are slightly different.


Once this happens, they begin to be bound by the forces of attraction between each molecule, but not entirely, so the gas then becomes a liquid. A good example of this is when a piece of glass or a mirror fogs up in a hot room. The vapour or steam in a room is a gas, and the glass or mirror is a colder material in comparison. Once the vapour hits the cold material, the energy within the vapour molecules is sapped out and into the mirror, warming it slightly.

Introduction to State Diagram

The abstraction of the attribute value is a property of the system, rather than a globally applicable rule. However, if the account balance would become negative after a withdrawal, the behavior of the withdraw function would be quite different. This is because the state of the bank account is changed from positive to negative; in technical jargon, a transition from the positive state to the negative state is fired. Are you looking for a Free UML tool for learning UML faster, easier and quicker?