[BNM] representing an OR aggregate/composite relation in UML class diagrams

[Jon Bedworth]

Actually, I have found the answer, in case anyone else is interested.

Specifically at :
http://www.essentialstrategies.com/publications/modeling/uml.htm

*Constraints between relationships*

Constraints between relationships are shown as dashed lines between pairs of
associations. Such a line is called a *constraint*. If it is annotated {xor}
or simply {or}, it is an "exclusive or". (Each occurrence of the base entity
must be (or may be) related to *either* an occurrence of one entity, *or* to
an occurrence of the other, *but not both*.) If it were {ior}, however, it
would be an "inclusive or". (Each occurrence of the base entity must be (or
may be) related to *either* an occurrence of one entity, *or* to an
occurrence of the other, *or both*.) Indeed, the dashed line can represent
any relationship desired between two associations.