Each data type property identifies whether and how that property is expected to be supported. Possible values, noted in italics in the data type specifications, are:
1. Not Permitted The property must never appear in an instance. Applications may raise an error if they receive it.
2. Optional The element may be supported by applications if they choose (and they must declare their decision in their conformance statement). If not supported, the element must be ignored if received. I.e. Applications MUST NOT raise an error upon receiving an unsupported optional element.
3. Required The property must be supported by all applications (they are able to capture and/or display it), but won’t necessarily always be present in an instance.
4. Populated The property must be supported (able to be captured and/or displayed) and must always appear in the instance, but may appear with a flavor of null.
The term 'populated' is not an official HL7 conformance strength. It was used in Canada to differentiate
Required 1..n (where a value must be supplied but can contain a flavour of null) from
Required 0..n (where no value need be supplied).
5. Mandatory The property must be supported and must always be present with a non-null value.
In general, if an attribute (or data type property) is not available (i.e. cannot be valued), then the rest of the data type properties (mandatory or not) should not be present. Exceptions to this rule will be documented in affected data types (e.g. CD).
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