Existence, occurrences, cardinality

Various issues exist in the 1.4 specification and the AOM regarding the constraint of existence of attributes, cardinality of container attributes and occurrences of classes within these containers. The UML of the relevant part of the Archetype Object Model is on the openEHR site.


The issue in relation to existence of attributes is described on the Developers' Wiki.


The issues with occurrences are:

  • Occurrences is mandatory in the AOM. This means some statement of occurrences is forced to be present even when there is no constraint.
  • The ADL parser (reference) sets this to 0..1 by default. Occurrences that are different from this are recorded.

Make occurrences optional and constraint statements are only necessary when occurrences deviates from the reference model.


The issue with cardinality is:

  • The ADL parser assumes cardinality is 0..* so even when there is no constraint, the cardinality of 0..* is entered into the ADL.

The reference parser should remove statements about cardinality unless they are explicitly expressed within the modelling environment.