# Addition of required / extensible / preferred / example terminology constraint to AOM and ADL

**URL:** https://discourse.openehr.org/t/addition-of-required-extensible-preferred-example-terminology-constraint-to-aom-and-adl/933
**Category:** ADL
**Created:** [19 August 2020 10:26 UTC](https://discourse.openehr.org/t/addition-of-required-extensible-preferred-example-terminology-constraint-to-aom-and-adl/933 "2020-08-19T10:26:59Z")
**Posts on this page:** 2
**Page:** 2

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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: [20 March 2023 14:13 UTC](https://discourse.openehr.org/t/addition-of-required-extensible-preferred-example-terminology-constraint-to-aom-and-adl/933/21 "2023-03-20T14:13:32Z")

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> [@pablo](#):
>
> is there anything to represent “not extensible”?

These are not flags but classifiers.

Here are the [FHIR definitions](https://www.hl7.org/fhir/terminologies.html#strength) (which we assume in openEHR).

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### Author: ![pablo](https://discourse.openehr.org/user_avatar/discourse.openehr.org/pablo/32/3505_2.png) [@pablo](https://discourse.openehr.org/u/pablo)
#### Post date: [20 March 2023 14:22 UTC](https://discourse.openehr.org/t/addition-of-required-extensible-preferred-example-terminology-constraint-to-aom-and-adl/933/22 "2023-03-20T14:22:50Z")

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I get it, `extensible` is what is User Defined Tables in HL7 v2.x vs. HL7 Defined Tables, which were two ways of expressing internal terminologies in HL7 v2.x messages. In some cases of User Defined Tables, HL7 v2.x specs actually provide a subset or sample table, for others the codes are 100% to be defined by the user.

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