The explicit modeling of relationships (besides parent/child) seems to be unique to CWE; it has not been handled in [7PK], [CLASP], or [Krsul].
CWE-1000 captures most of the chains and composites in CWE. Since CWE-699 is more developer-friendly, it generally does not specify those relationships, although they are readily visible on the CWE web site.
Even if mutual exclusiveness is ultimately achieved, modeling inter-relationships would still be useful. For example, in biological classification, humans and dogs aren't in the same Order, but their association with each other is notable enough to be recorded.
Accepted