UML14 — Modeling of guards

Summary: Guard is a class, but it could have been modeled as an attribute in
Transition, with the type BooleanExpression.
If it is left as a stand-alone class, it doesn"t have to inherit from
ModelElement, especially since ModelElement has many associations, and
Guard
doesn"t use them at all. In fact this is more or less the case with many
other descendants from ModelElement (for example, an Association doesn"t
use
the following associations inherited from ModelElement: behavior
(towards
StateMachine), collaboration (towards Collaboration) ).

Considered and declined.