# openEHR-technical Digest, Vol 33, Issue 3

**Category:** [Technical (archive)](https://discourse.openehr.org/c/technical-archive/156)
**Created:** 2009-04-02 11:00 UTC
**Views:** 6
**Replies:** 0
**URL:** https://discourse.openehr.org/t/openehr-technical-digest-vol-33-issue-3/13259

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## Post #1 by @Greg_Caulton

>
> Message: 5
> Date: Thu, 2 Apr 2009 10:53:04 \+0200
> From: Rong Chen <rong\.acode@gmail\.com>
> Subject: Re: Question about the item property of Item\_Tree
> To: For openEHR technical discussions <openehr\-technical@openehr\.org>
> Message\-ID:
>        <ebd0d070904020153y4bac0b48yb794a8b7fa2885d8@mail\.gmail\.com>
> Content\-Type: text/plain; charset=ISO\-8859\-1
>
> Hi Seref,
>
> Interesting thought\! I think this comes down to a design choice, which
> is whether we want to force single\-rooted tree\. By definition, tree
> data structure has a single root\. But when we model hierarchical
> structure of clinical content, it's convenient to allow multiple nodes
> at the top level of the tree without the need to create a root node
> just to satisfy the notion of single\-rooted tree\. So it's a choice
> between purity \(according to computer science definition of a tree\)
> and convenience \(which somewhat indirectly translated to usability of
> the model and relevant tools\)\.
>
> Cheers,
> Rong
>
Not sure if it helps in the design but in Java \(Swing\) the JTree
control's model has a tree data structure \(per comp sci definition\)
but to display a multiple top level nodes you can mark the root node
as hidden\.

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**Canonical:** https://discourse.openehr.org/t/openehr-technical-digest-vol-33-issue-3/13259
**Original content:** https://discourse.openehr.org/t/openehr-technical-digest-vol-33-issue-3/13259