UML State Diagrams

In the previous chapters, we described business processes and sub-processes using activities, rules, and outcomes. We also used diagrams to show how work is performed.

In this chapter, we look at a different kind of diagram that focuses on states and how a process moves between them.

State Diagrams

A UML State Diagram describes a process or sub-process in terms of states. At any given moment, the process is in exactly one state and remains there until something causes it to move to another state.

A state can be understood as a waiting condition. While the process is in a state, nothing happens until a triggering event occurs.

Transitions

When a process moves from one state to another, this movement is called a transition.

A transition represents the execution of a set of activities performed according to business rules that move a process from its current state to a target state.

For example, verifying a health card may lead to different outcomes depending on the verification result.

The diagram below shows the “Person Identification” sub-process of a dental office information system using a clear, consolidated view:

You can read a state diagram by following the arrows: the process waits in a state, then a trigger causes a transition, and rules determine which target state is reached.

Why State Diagrams Matter

State diagrams make it easy to see how a process behaves over time. They show where a process waits, what events move it forward, and what outcomes are possible.

This makes them especially useful when precise behavior matters, such as when modeling long-running business processes or implementing them in software.

In the next chapter, we will connect these ideas to a simple concept used in software: the finite state machine.

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