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13.3.7 ChangeEvent


   A change event models a change in the system configuration that makes a condition true.



    Event (from Communications ) on page 459


   A change event occurs when a Boolean-valued expression becomes true. For example, as a result of a change in the value held in a slot corresponding to an attribute, or a change in the value referenced by a link corresponding to an association. A change event is raised implicitly and is not the result of an explicit action.


   No additional attributes


Issue 8302 -add subsets constraint

changeExpression: Expression [1] A Boolean-valued expression that will result in a change event whenever its value changes from false to true. {Subsets Element::ownedElement}
No additional constraints

   Each time the value of the change expression changes from false to true, a change event is generated.

   Semantic Variation Points

   It is a semantic variation when the change expression is evaluated. For example, the change expression may be continuously evaluated until it becomes true. It is further a semantic variation whether a change event remains until it is consumed, even if the change expression changes to false after a change event.


   A change event is denoted in a trigger by a Boolean expression.

   <change-event> ::= ‘when’ <expression>

   Changes from previous UML

   This metaclass replaces change event.