M_ASSOCIATION_BY_REFERENCE An instance of class A is associated with zero or more instances of class B. The B instances may be referenced by more than one instance of A. This is the most general form of association and is the default if no type is specified.
M_ASSOCIATION_BY_CONTAINMENT Implies that an instance of class A "owns" one or more instances of class B. No other class has ownership of the same B instance. If class A is deleted, logically the B instance should be deleted also.
M_ASSOCIATION_BY_CONSTRAINT_REF An instance of class A and an instance of class B together contain enough key information to uniquely associate them with an instance of class C. Deletion of A or B instances should cause deletion of all C instances which are no longer referenced. The relation of A or B to C is of type CONSTRAINT_REF