# Msg#4 - Software Archetypes - single vs double systems

**Category:** [Technical (archive)](https://discourse.openehr.org/c/technical-archive/156)
**Created:** 2006-04-10 17:51 UTC
**Views:** 3
**Replies:** 1
**URL:** https://discourse.openehr.org/t/msg-4-software-archetypes-single-vs-double-systems/14133

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## Post #1 by @Bill_Walton

systems

> What I find most frustrating about discussion of archetypes is that it
> is so often vague and intuitive in nature, making it rather hard to
> decipher\.
>
> > Software Archetypes \- single vs double systemsHi Lorie,
> >
> > Archetypes provide a capability that's very familiar to programmers,
> > but take it to the next level\.  At the most basic level, it's about
> > decoupling\.  An RDBMS shields programs from the need to know about
> > the underlying structure of the data\.  A program needs only know
> > about the db schema\.  Views provide another level of abstraction,
> > shielding programs from changes in the schema\.  Archetypes \(which I
> > believe do not depend on an RDBMS implementation\) provide a similar
> > capability, but take it to the domain level\.
>
> By domain do you mean application domain? Or are you referring to
> domains in their technical sense in database theory \(as a set of
> values\)? At any rate, it is clear that you are trying to abstract away
> from a particular set of units, treating the quantity itself as a value
> \(not how it might be represented\)\.
>
> >
> > When working with an archetype\-enabled system, programs / programmers
> > work directly with domain concepts like blood pressure or height or
> > weight\.  The underlying data is stored / accessed through the
> > archetype\.
>
> But what does this mean? It suggests that an archetype is realizable as
> a computational object \(much as a schema may be realized as a set of
> relations, or a class instantiated to form an object\)\. I suspect that
> this is the point at which an important concept is missing: The
> integers are a ring, but when I add two numbers, I'm not using the \+
> operation of the category Ring, but rather of a specific member of that
> category, namely Z\.
>
> > A trivial example of the benefits would be lbs\. vs\. kgs\.\.
> >  In an archetype\-enabled system, the program has no knowledge of the
> > unit\-of\-weight measure used to store the data\.  Programs access the
> > data store with statements like \(no representation made re: syntax\)
> > store\_weight\(220, lbs\) and patient\_weight =
> > retrieve\_weight\(patient\_id, kgs\)\.
>
> Okay, here is some concrete syntax, but what are you really doing? Is
> kgs a flag or map \(or something else altogether\)? From a mathematical
> point of view, it's natural to think of it as a scaling transformation
> \(a map\)\. But that's  confusing, too, because it implies the existence
> of some reference instance out there \(say kilograms\) that is somehow
> privileged among other possible choices, and that your kgs flag is
> simply the scaling factor \(isomorphism\) you need to apply to get your
> chosen representation\.
> >
> > You might want to take a look at
> > http://oceaninformatics.biz/archetypes/MindMap/ArchetypeMap.html for
> > a better, high\-level understanding of the above\.  This, and a good
> > deal of the related stuff, will be migrated shortly to the openEHR
> > site\.
> >
> > Be happy to provide / get you more in\-depth info if desired\.
> >
> > hth,
> >
>
> ===
> Gregory Woodhouse  <gregory\.woodhouse@sbcglobal\.net>
>
> "It is foolish to answer a question that
> you do not understand\."
> \-\-G\. Polya \("How to Solve It"\)
>
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## Post #2 by @thomas.beale

Some answers that may or may not be useful for the hardhats\.

Bill Walton wrote:
> From: "Greg Woodhouse" <gregory\.woodhouse@sbcglobal\.net>
> To: <hardhats\-members@lists\.sourceforge\.net>
> Sent: 2006\-04\-10 10:46 AM
> Subject: Re: \[Hardhats\-members\] Software Archetypes \- single vs double
> systems
>
>> What I find most frustrating about discussion of archetypes is that it
>> is so often vague and intuitive in nature, making it rather hard to
>> decipher\.
>>
>>> Software Archetypes \- single vs double systemsHi Lorie,
>>>
>>> Archetypes provide a capability that's very familiar to programmers,
>>> but take it to the next level\.  At the most basic level, it's about
>>> decoupling\.  An RDBMS shields programs from the need to know about
>>> the underlying structure of the data\.  A program needs only know
>>> about the db schema\.  Views provide another level of abstraction,
>>> shielding programs from changes in the schema\.  Archetypes \(which I
>>> believe do not depend on an RDBMS implementation\) provide a similar
>>> capability, but take it to the domain level\.
>>>      
>>
>> By domain do you mean application domain? Or are you referring to
>> domains in their technical sense in database theory \(as a set of
>> values\)?

application domain\. It means you can consider an archetype as a model of some domain concept, like "microbiology test result", that a health care professional can understand \(and define\)\.
>>  At any rate, it is clear that you are trying to abstract away
>> from a particular set of units, treating the quantity itself as a value
>> \(not how it might be represented\)\.
>>
>>> When working with an archetype\-enabled system, programs / programmers
>>> work directly with domain concepts like blood pressure or height or
>>> weight\.  The underlying data is stored / accessed through the
>>> archetype\.
>>>      
>>
>> But what does this mean? It suggests that an archetype is realizable as
>> a computational object \(much as a schema may be realized as a set of
>>    

it is\. The model of all archetypes is given at http://svn.openehr.org/specification/TRUNK/publishing/architecture/am/aom.pdf
or if you want online UML, see http://www.openehr.org/uml/Browsable/_9_0_76d0249_1108467924943_474004_589Report.html
>> relations, or a class instantiated to form an object\)\. I suspect that
>> this is the point at which an important concept is missing: The
>> integers are a ring, but when I add two numbers, I'm not using the \+
>> operation of the category Ring, but rather of a specific member of that
>> category, namely Z\.
>>
>>> A trivial example of the benefits would be lbs\. vs\. kgs\.\.
>>>  In an archetype\-enabled system, the program has no knowledge of the
>>> unit\-of\-weight measure used to store the data\.  Programs access the
>>> data store with statements like \(no representation made re: syntax\)
>>> store\_weight\(220, lbs\) and patient\_weight =
>>> retrieve\_weight\(patient\_id, kgs\)\.
>>>      
>>
>> Okay, here is some concrete syntax, but what are you really doing? Is
>> kgs a flag or map \(or something else altogether\)? From a mathematical
>> point of view, it's natural to think of it as a scaling transformation
>> \(a map\)\. But that's  confusing, too, because it implies the existence
>> of some reference instance out there \(say kilograms\) that is somehow
>> privileged among other possible choices, and that your kgs flag is
>> simply the scaling factor \(isomorphism\) you need to apply to get your
>> chosen representation\.
>>    

it is not that complicated\. The archetype simply constrains a QUANTITY object which is defined by a QUANTITY class\. The openEHR model of this class is here: http://www.openehr.org/uml/Browsable/_9_0_76d0249_1109599337877_94556_1510Report.html

There is a custom C\_QUANTITY constrainer class that can be used as well, which is particularly suitable for constraining values in multiple unit systems\.
See this test archetype: http://my.openehr.org/wsvn/knowledge/archetypes/dev/adl/test/clinical_types/adl-test-entry.c_quantity.draft.html?op=file&rev=0&sc=0
That's raw ADL of course; in the clinician's archetype editor it is done via a GUI\.

\- thomas beale

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**Canonical:** https://discourse.openehr.org/t/msg-4-software-archetypes-single-vs-double-systems/14133
**Original content:** https://discourse.openehr.org/t/msg-4-software-archetypes-single-vs-double-systems/14133