# openEHR-technical Digest, Vol 32, Issue 14

**Category:** [Technical (archive)](https://discourse.openehr.org/c/technical-archive/156)
**Created:** 2009-03-20 23:44 UTC
**Views:** 7
**Replies:** 1
**URL:** https://discourse.openehr.org/t/openehr-technical-digest-vol-32-issue-14/13166

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## Post #1 by @Greg_Caulton

It makes sense, but I will have to find time to dig into the
differences between the EHR and Demographic reference model classes
and understand why they need to be different\.

And then determine once we have added one more reference model class,
how many more will need to be added to achieve a standalone HIS to
address administrative processes \- billing, admission, discharge etc\.

At this point it doesn't seem to make sense to build a new
administrative reference model for the non\-EHR content\.   Better to
stick with HL7 and other standards than to reinvent the wheel\.

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## Post #2 by @thomas.beale

Greg Caulton wrote:
> It makes sense, but I will have to find time to dig into the
> differences between the EHR and Demographic reference model classes
> and understand why they need to be different\.
>  
Greg,
you can see the demographic model at
http://www.openehr.org/uml/release-1.0.1/Browsable/_9_5_76d0249_1118674798473_6021_0Report.html
; you will see that the lower structural classes like ITEM\_STRUCTURE,
all the data types etc are shared across the demographic and EHR models
\(all the models are at
http://www.openehr.org/svn/specification/TAGS/Release-1.0.1/publishing/architecture/computable/UML/uml_start_view.html)

It's all the same reference model really, just different upper parts of
it for different business purposes\.

> And then determine once we have added one more reference model class,
> how many more will need to be added to achieve a standalone HIS to
> address administrative processes \- billing, admission, discharge etc\.
>
> At this point it doesn't seem to make sense to build a new
> administrative reference model for the non\-EHR content\.   Better to
> stick with HL7 and other standards than to reinvent the wheel\.
>  
not that this is likely to happen in the short term, but HL7 doesn't
have any non\-message oriented, archetype\-enabled models for any of the
above\.\.\.

\- thomas beale

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**Canonical:** https://discourse.openehr.org/t/openehr-technical-digest-vol-32-issue-14/13166
**Original content:** https://discourse.openehr.org/t/openehr-technical-digest-vol-32-issue-14/13166