> At the moment we have not seen any need for multiple inheritance in > archetypes.
I see this as very similar to multiple inheritance in objects. There is no *need*, but there is useful things that can be done. The question is whether the price is justified. The use case is relatively simple in concept - allowing multiple inheritance would allow me to "cross-cut" concerns. I could write an archetype that only dealt a narrow aspect of an information structure, such as data integrity issues, and then use it across multiple archetypes, letting them focus on the big picture, not the minutiae of data integrity, which is mostly overlooked but ubiquitiously present. This would surely be useful for some things. The problem is the price. How do you manage it, how would you use it, what does it mean to allow "multiple inheritance". The archetype cannot allow anything not allowed in all it's parents - so they have to "allow" some fairly generic structures. To actually use it in an instance, the instance is now making claims that become very much more difficult to evaluate. HL7 templates are an approach to solving this problem. HL7 static models allow for multiple inheritance, though this can be discovered (some controversy where discovery safe though). Actually, given the similarity between static models and AOM, it's possible that the algorithm that HL7 uses would be applicable to AOM too. Because HL7 models allow multiple inheritance by discovery, it is also necessary to represent the multiple applicable constraint models in the instance, greatly complicating the instance and the processing of the instance. However there are some interesting design patterns that can arise, and that are arising, in the HL7 space as a consequence of this. So, resist any thought of multiple inheritance in openEHR - it will greatly complicate matters. Let HL7 find out whether templates represent a great big hole to fall into, or whether they will be truly enabling. (btw what I have described is not all that templates are in HL7, so the mere fact that templates are successful, particularly in CDA, is not evidence that multiple inheritance can be made to work) Grahame
