UML25 — Pg. 613, Clause 17.3.4: Notation

Title: Incomplete grammar for “<lifelineident>” in Clause 17.3.4
Summary: This clause specifies the following grammar for “<lifelineident>”:

<lifelineident> ::= ([<connectable-element-name>[‘[‘<selector>‘]’]] [: <class_name>][decomposition]) | ‘self’

“<class_name>”, however, is too restrictive for the type. A lifeline may represent an instance of an Actor, not just an instance of a Class. In fact, the metamodel, as written, allows a lifeline to represent an instance of any type of BehavioredClassifier. Here are the relationships:

A lifeline represents 0..1 instances of ConnectableElement.
ConnectableElement is a type of TypedElement.
TypedElement has an association with 0..1 instances of Type.
BehavioredClassifier is a type of Classifier, which is a type of Type.
BehavioredClassifier has 4 specializations: Class, Actor, UseCase, and Collaboration.

Therefore, any of these 4 subtypes may serve as the type of the connectable element that a lifeline represents. But only 2 of these make sense in the context of a lifeline: Class and Actor. So there are really 2 problems that need to be resolved. Recommendations provided below

Proposed Resolution:
1) The grammar for “<lifelineident>” needs to be expanded to allow for an actor to serve as the type of the connectable element that a lifeline represents, and
2) A constraint needs to be introduced to allow only two of the four subtypes of BehavioredClassifier to serve as the type of the connectable element that a lifeline represents.

Merged with 18748