The EHR class includes subject and time_created. But there is a need for
an ehr_id distinct from the subject id. All EHRs have their own id, but
in reality, two EHRs could have the same subject id, due to errors that
occur in real systems, data entry etc. Also, subject id needs to be
versioned (sometimes it turns out that the data of the EHR is correct, but
the subject id has to be changed, e.g. the current one is a duplicate for
the same patient and is being dropped).
Aloso, currently there is no clear place to store EHR management data e.g.
patient inactive / not under care (therefore cancel notifications)
Creating a standardised versioned object for this purpose would allow
EHR-level atributes to be versioned, and openEHR software to interoperate
with data in different EHRs.