# HISTORY, ITEM\_TREE and other LOCATABLE at-codes

**URL:** https://discourse.openehr.org/t/history-item-tree-and-other-locatable-at-codes/12725
**Category:** Implementers (archive)
**Created:** [31 May 2011 11:12 UTC](https://discourse.openehr.org/t/history-item-tree-and-other-locatable-at-codes/12725 "2011-05-31T11:12:40Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![Justinas\_Prelgauskas](https://discourse.openehr.org/letter_avatar_proxy/v4/letter/j/b487fb/32.png) [@Justinas\_Prelgauskas](https://discourse.openehr.org/u/Justinas_Prelgauskas)
#### Post date: [31 May 2011 11:12 UTC](https://discourse.openehr.org/t/history-item-tree-and-other-locatable-at-codes/12725/1 "2011-05-31T11:12:40Z")

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Hello,

I’ve been looking through a very useful set of ADL 1.5 test archetypes related to Specialization feature of OpenEHR via “Knowledge2” repository ( [http://www.openehr.org/wsvn/knowledge2/TRUNK/archetypes/ADL\_1.5\_test/validity/specialisation](http://www.openehr.org/wsvn/knowledge2/TRUNK/archetypes/ADL_1.5_test/validity/specialisation) ).

I think some of archetype nodes lack “at”-codes.  
For example OBSERVATION archetype “openEHR-EHR-OBSERVATION.spec\_test\_obs.v1” uses such types as HISTORY and ITEM\_TREE.  
However, both HISTORY and ITEM\_TREE types are LOCATABLE.  
Thus I think all such objects must have “at”-codes declared.  
This must be true for all LOCATABLE objects, because they have mandatory property “archetype\_node\_id”.  
Or maybe I am missing something?

Regards,  
Justinas Prelgauskas

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### Author: ![thomas.beale](https://discourse.openehr.org/user_avatar/discourse.openehr.org/thomas.beale/32/35_2.png) [@thomas.beale](https://discourse.openehr.org/u/thomas.beale)
#### Post date: [1 June 2011 16:13 UTC](https://discourse.openehr.org/t/history-item-tree-and-other-locatable-at-codes/12725/2 "2011-06-01T16:13:20Z")

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Justinas,

the currently proposed rules for ADL1.5 (see the draft), see section 5.3.12 are that at-codes are optional. This allows many leaf and near-leaf level nodes not to have to have useless at-codes attached to them. The same goes for any node that is a single child of an attribute, like HISTORY etc. The motivation for this is to allow for simpler paths, and keep the size of archetypes down to what is needed.

The C\_OBJECT.node\_id property is mandatory in the AOM. What we do in the current implementations is that the node\_id is set to the value ‘unknown’. This is currently not properly specified in the spec, but is implemented in the [ADL workbench](http://www.openehr.org/svn/ref_impl_eiffel/TRUNK/apps/adl_workbench/doc/web/index.html).

hope this helps

- thomas