Provider needs to be optional on ENTRY, otherwise it will cause massive
issues with integration of legacy data and being a participation rather
than a party_ref means that it is not simple as the mode has to be set.
We should leave this to grow organically for the time being -
it will usually be left blank in all but the most rigorous systems.

The term "provider" in health usually means the healthcare provider so
I am sure this will be filled in with the doctor's details - and will
mean the patient is not usually given. This is appropriate for instruction
and evaluation, but not for observation. In fact, if it is optional
that will be fine as you will usually only want to record the provider
anyway (mode of patient is a bit dumb as is adding the patient demographic
here!)