What does "subsets" mean in UML exactly?

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The UML 2.5.1 specification does not define the keyword subsets very well. I found the following in section 6.4.2:

The constraint {subsets endA} means that the association end to which this constraint is applied subsets the association end endA.

Consider the following diagram:

subsets-example

Intuitively, I would think this means the following:

  1. A Person can be a member of zero or more Clubs.
  2. A Person can be the leader of at most one Club.
  3. If a Person is the leader of a Club, then he/she is also a member of the same Club.
  4. If a Person is the leader of a Club, then he/she can still be a member of other Clubs at the same time.

I wonder if statement 4 is correct. In a discussion with Jim L. in the comments under his answer to another question, Jim wrote

You can’t restrict the cardinality of a subset and still have an element of the superset that violates the restriction.

If I understand this well, if a Person is the leader of a Club, then he/she cannot be a member of another Club.

Is there some place in the UML specs that defines subsets better than what I found?



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