Above is a class diagram extracted from Chapter 11 - UML and Programming of Martin Fowler's UML Distilled. I have a question about the multiplicity on Phenomenon Type in associations with Measurement and Phenomenon. Why a Phenomenon may not have a PhenomenonType while a Measurement must have a PhenomenonType? Can anybody give me a example of any Phenomenon that can not have a PhenomenonType associated with it in term of Patient Observation? TIA. makah