# Occurrences on Top level element

**Category:** [Clinical (archive)](https://discourse.openehr.org/c/clinical-archive/153)
**Created:** 2017-10-27 22:47 UTC
**Views:** 1
**Replies:** 2
**URL:** https://discourse.openehr.org/t/occurrences-on-top-level-element/14362

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## Post #1 by @leonardo_ornelas

Hello, my name is Leonardo Ornelas, this is my first message for this mail list. Maybe somebody could take my doubts. I'm working on a project that follows some parts of openEHR. I did an adl-core implementation on nodejs. This version makes the parser from adl to json, supports flattener of archetypes and generation of operational templates, as well as the generation of a hierarchical model of RM from Archetype / OPT. There is a person in the team in charge of creating some templates and archetypes for our needs, which led to a questioning about occurrences that he could not answer. I looked in the document but could not find it on. I wonder if in the RM model it is possible to have occurrences of a element that is root? Eg. If a CLUSTER is the first element of an archetype that cluster could have occurrence 0 .. * or 1 .. *.

Could the following ADL be valid?
...
definition
EVALUATION [id1.1] matches occurrences matches {0..2} matches {
...

In that case, in the RM model, when in the form add a new element, could I have an EVALUDATION with the same archetype_node_id?

Thanks in advance.

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## Post #2 by @system

Hi Leonardo

I think such a constraint usually belongs in the container. Do you have an example?

Cheers, Sam

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## Post #3 by @system

Sam is right. The occurrences of an archetype root is always {1..1}. In the container of that archetype (an archetype slot) you can redefine those occurrences.

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**Canonical:** https://discourse.openehr.org/t/occurrences-on-top-level-element/14362
**Original content:** https://discourse.openehr.org/t/occurrences-on-top-level-element/14362