When I was trying to validate an archetype with the reference model
(openEHR-EHR-OBSERVATION.apgar), I found something strange on all
'event' archetypes.
The EVENT class has a function (method) that calculates the offset.
However, in that archetype the offset was restricted as if it was an
attribute.
What is the sense for this? Shouldn't this restriction be expressed as
an assertion over the different attributes? (that is, a restriction
that must be checked at runtime as it is a result from a method).
