*UK LOM Core, Null values (summary)*
The following is a summary of discussion on the CETIS-Metadata list, and
will hopefully serve as the agreed starting point for further discussion at
the UK LOM Core meeting in Glasgow. The archives of the original discussion
can be found at http://www.jiscmail.ac.uk/lists/cetis-metadata.html (the
discussion took place in July).
*Position in UK LOM Core draft 2*
From Recommendations section (p3)
"In order for a UK LOM Core instance to be valid, values must be supplied
for all mandatory elements"
*Issue Description*
Is a null value a valid value?
Andy Powell wrote (at 16:32 on Fri 9 July, Subject: UK LOM Core: mandatory
elements)
"The other argument against making so many elements mandatory is that for
all elements (with the possible exceptions of the identifiers) there will
be some scenarios in which the element has no valid value. In such cases,
the only course of action is to provide the element with a null value? I
assume that a null value is legal(?) but doing this seems, to me, to
completely undermine what is being attempted by trying to mandate
particular elements. Why is an empty value OK but a missing element is
not?"
Andrew Middleton wrote (at 11:18 on Tue 13 July, Subject: Re: UK LOM Core:
mandatory elements)
"Why is it OK to have mandatory elements that are empty? I always thought
this was a technical interoperability issue, that some systems could not
deal with missing elements - they expect the element to appear in the
structure, yet the value (including none) is irrelevant. I don't know...
"So my view is that mandatory is OK if it enhances the interoperability -
as long as it's OK for elements to be left empty."
Scott Wilson wrote (at 11:57 on Tue 13 Jul, Subject Re: UK LOM Core:
mandatory elements)
"IMHO, if a field is mandatory, a blank value isn't valid. If you are going
to create an empty node, better just to omit the node - if that throws a
processing error, well so SHOULD an empty node, if the coder of the target
system has properly handled such things."
*Routes to Resolution?*
I think it's a simple yes/no choice, which should depend on the reason for
mandating elements.
Any other suggestions?
Phil.
--
Phil Barker Learning Technology Adviser
ICBL, School of Mathematical and Computer Sciences
Mountbatten Building, Heriot-Watt University,
Edinburgh, EH14 4AS
Tel: 0131 451 3278 Fax: 0131 451 3327
Web: http://www.icbl.hw.ac.uk/~philb/
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