The HL7V3 R2 abstract Datatypes would appear to be the logical datatypes to use in a VMR representation. Ideally they will be aligned with the ISO datatypes. The UK NHS "Logical Record Architecture" uses these and CDA V3 would use these. It would be possible to map older data onto the new datatypes and the NULL flavour attributes are very useful in detecting absent data, rather than an empty list.

Current HL7 V3 datatype Specification