Hello Martin, David, all,

Martin raises an relevant point, even though it took me minute or two to see 
the difference.

Now :"The only CF standard attribute which is allowed to refer to external 
variables is cell_measures."
meaning that that only the CF standard attribute cell_measures is allowed to 
make reference external variables (as well as any non-CF standard attributes of 
course).

Martins suggestion: "The only attribute which is allowed to make a CF standard 
reference to external variables is cell_measures"
allows any of the 'free text' CF standard attributes to refer to external 
variables, but such reference will not be understood by software (as anything 
else in the free text attributes)

In both cases the intended meaning is preserved that a cell_method reference to 
an external variable will be understood by software.

I support Martin's suggestion.

Kind regards,
Lars




-----Original Message-----
From: CF-metadata [mailto:[email protected]] On Behalf Of 
[email protected]
Sent: den 5 april 2017 12:57
To: [email protected]
Cc: [email protected]
Subject: Re: [CF-metadata] Overstated restriction on references to external 
variables in version 1.7

Hi David,

my point is indeed that you should be able to put anything in them, so have a 
standards document which says that you can't put references to external 
variables in them would be a mistake .....

cheers,
Martin

________________________________
From: David Hassell [[email protected]]
Sent: 05 April 2017 11:35
To: Juckes, Martin (STFC,RAL,RALSP)
Cc: CF Metadata
Subject: Re: [CF-metadata] Overstated restriction on references to external 
variables in version 1.7

Hello Martin,

I don't quite see what you mean - such attributes are non-standardised, so you 
can already put anything you like in them, but software won't be able to do 
anything about it. Could you perhaps give a CDL example?

Many thanks,

David

On 5 April 2017 at 09:36, 
<[email protected]<mailto:[email protected]>> wrote:
Hello All,

Section 2.6.3, External Variables, of version 1.7 of the standard contains the 
statement that:"The only CF standard attribute which is allowed to refer to 
external variables is cell_measures."

I believe this is stronger than intended: it should be possible, for instance, 
to refer to external variables in the comment and history attributes, and any 
other free text attribute, or the comment part of the cell_methods string.

Should it say something along the lines of:
"The only attribute which is allowed to make a CF standard reference to 
external variables is cell_measures"?

regards,
Martin

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--
David Hassell
National Centre for Atmospheric Science
Department of Meteorology, University of Reading, Earley Gate, PO Box 243, 
Reading RG6 6BB
Tel: +44 118 378 5613
http://www.met.reading.ac.uk/
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