Add a controlled vocabulary for unknown/empty values

[eli-blazek]

Description

It would be really useful to have a standardized set of values describing unknown/empty values in metadata fields. With every database, every programming language and every programming tool implementing their own equivalent for None/empty value (consider NaN, NULL, Null, None, \0 etc.), there is a risk of filtering/accounting for those values becoming unmanageable

Proposed solution

We, as methodical support for NRP repositories suggest using/adapting DataCite's Standard Values for Unknown information controlled vocabulary for limiting unknown/empty/null values:

Code	Definition
:unac	temporarily inaccessible
:unal	unallowed, suppressed intentionally
:unap	not applicable, makes no sense
:unas	value unassigned (e.g., Untitled)
:unav	value unavailable, possibly unknown
:unkn	known to be unknown (e.g., Anonymous, Inconnue)
:none	never had a value, never will
:null	explicitly and meaningfully empty
:tba	to be assigned or announced later
:etal	too numerous to list (et alia)

[MichalMed]

I would definitely go in the way of controlled vocabulary identified with iris.

[Wyvi]

@MichalMed Could you please clarify how empty values in CCMM, particularly for string attributes such as the name of an Agent, are intended to be filled using an IRI identifier? I suggest that the usage of these empty values will be explicitly detailed within the methodology not in controlled vocabulary.

[MichalMed]

The usage in the end is to identify the same value based on its meaning. This is what controlled vocabularies were made for.