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#74: Allow sharing of ancillary variables among multiple data variables
---------------------------------------+------------------------------------
  Reporter:  [email protected]  |       Owner:  
[email protected]             
      Type:  enhancement               |      Status:  new                      
                 
  Priority:  medium                    |   Milestone:                           
                 
 Component:  cf-conventions            |     Version:                           
                 
Resolution:                            |    Keywords:  "ancillary data" 
"standard name modifiers"
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Comment (by mgschultz):

 Dear all,

 I am all for this proposal. Only, I would like to raise one more technical
 point, i.e. we should define the proper way for parsing a standard_name
 with this extension. If I am not mistaken, then the current proposal
 mandates to read a standard_name attribute from right to left, checking
 first if the rightmost part is actually a standard_name modifier. If so,
 then one or more standard_names (separated by blanks) are allowed to the
 left. If the rightmost string is no standard_name modifier, it is supposed
 to be a standard_name and must be one string (i.e. no blanks).

 For a moment, I was wondering whether it would make sense to think a
 little broader and introduce the concept of a "standard_name pointer",
 meaning that - through a modifier - the variable content is no longer
 referring to a quantity that is described by the standard_name itself, but
 the standard_names that are listed, are merely references to variables
 with that content. It may then be useful to indicate this explicitly in
 the syntax, for example, by prepending a "*" as in the C language, or a
 more xml-style identifier such as "X:". The example given at the top of
 this thread would then become:

 {{{
 int nobs(lat,lon);

     . . nobs:standard_name="X:sea_water_potential_temperature
 sea_water_salinity number_of_observations"; . .
 }}}

 ... and then it would probably be easier to understand if the modifier
 would come first, followed by the list of variables to which it refers,
 i.e.:

 {{{
 int nobs(lat,lon);

     . . nobs:standard_name="X:number_of_observations
 sea_water_potential_temperature sea_water_salinity"; . .
 }}}

 I realize, this is a more radical change. If there are sympathies for
 this, then we should perhaps schedule it for CF 2.0?

 Best,

 Martin

-- 
Ticket URL: <https://cf-pcmdi.llnl.gov/trac/ticket/74#comment:23>
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