Currently existence, occurrences and cardinality are all mandatory in the AOM. However, with reference model checking, this is not required. Existence and cardinality should only be stated when they override, i.e. narrow the reference model value. Occurrences should only be stated when it overrides the RM cardinality for multiply-valued attributes, or existence, for single-valued attributes. E.g. if the cardinality for a multuply-valued attribute is 0.., then the occurrences will be assumed to be 0.. on each member Object in an archetype unless otherwise stated.