Once you have a state-machine-attribute you will get a state-diagram for it. The State diagram contains States are the only allowed values of the state attribute string.

The state diagram also defines transitions between these states.

This brings structure in many ways:

1. Only a limited set of values are possible
2. Change between values must follow the defined order
3. You may have rules (guards) that must be fulfilled in order to allow transition
4. You can add "things to happen" when you enter a state

A class may have many state-attributes, but each state must be uniquely named within the class - this is because we can ask an object "self.oclIsInState(#SomeState)" regardless of attribute holding the state.

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