Andrew Patterson wrote:
> For the case where an attribute is constrained to '0'
> existence i.e.
>
> state existence matches {0} .....
>
> what should follow as the rest of the attribute
> constraint? Technically, the rest of the definition
> is superfluous as we have already stated that the
> attribute must not exist, but the
> 'matches' clause needs to exist in the grammar. Should
> it be matched to *, or should it be empty?
>
> state existence matches {0} matches {*}
>
> or
>
> state existence matches {0} matches {}
> (I'm not sure the grammar allows this)
>
we certainly have not allowed for it yet; indeed, no-one has ever wanted
to do it in an archetype, it has only come up as a need in templates
(which simply quote path names and then add an existence constraint).
Possible responses that come to mind:
- in openEHR we try never to include a feature that is not justified by
at least one known use case. So we should try to find a real use case
before doing anything.
- there is in fact already a way to do this: by adding an invariant to
an archetype of the form
not exists (/path/to/some/attribute/that/we/dont/want)
- if we had to add more syntax to the cADL part of ADL, I would probably
opt for the second proposal above.
But....a credible use case needs to be found first.
- thomas beale
> Andrew
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>
>
--
___________________________________________________________________________________
CTO Ocean Informatics (http://www.OceanInformatics.biz)
Research Fellow, University College London (http://www.chime.ucl.ac.uk)
Chair Architectural Review Board, openEHR (http://www.openEHR.org)
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