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#104: Clarify the interpretation of scalar coordinate variables
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  Reporter:  jonathan        |       Owner:  [email protected]
      Type:  defect          |      Status:  new                          
  Priority:  medium          |   Milestone:                               
 Component:  cf-conventions  |     Version:                               
Resolution:                  |    Keywords:                               
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Comment (by jonathan):

 Dear Ed and Mark

 As you know, this is a long-running discussion with Mark. However, I
 maintain that what David and I propose here is what the convention is
 intended to mean. Firstly, this is because I am confident that it's what
 the authors of the convention had in mind when scalar coordinate variables
 were invented. Of course memories are not perfect, so I cannot be certain,
 but that's my honest recollection. Secondly, I think it is the most
 obvious interpretation of the words as they stand now. If we wanted to
 introduce a conceptually different kind of coordinate variable, it would
 be misleading to write, "Scalar coordinate variables have the same
 information content and can be used in the same contexts as a size one
 coordinate variable." I would say that the evident intention of that
 statement is that scalar coordinate variables ''mean'' the same as size
 one coordinate variables (not size one auxiliary coordinate variables).
 Thirdly, it is sufficient to have two abstract kinds of coordinate
 variable, and because it is simpler it should be preferred.

 David and I propose these changes because Mark suggests an alternative
 interpretation, which would not be what the convention was intended to
 mean, and which we would therefore like to exclude. Our aim is to clarify
 the intention of the CF document. That is why this is a defect ticket. The
 document is erroneous in apparently allowing an interpretation which was
 not intended.

 Your arguments are concerned with flexibility in the interpretation of CF-
 compliant data. I think that's a different matter from what the convention
 means. It's fine to reinterpret data as part of analysing or processing
 it. That's a routine thing to do. Therefore our statement of what the
 convention means does not prevent your interpretation of CF-compliant
 data. I wrote about this on [http://mailman.cgd.ucar.edu/pipermail/cf-
 metadata/2013/056615.html the email list]. It would be interesting to know
 your response to that (on the email list). I appreciate that you would be
 rightly concerned if there was a loss of flexibility, but I really don't
 think you need to be. You can offer the user of software a flexibility in
 interpreting scalar coordinate variables, if you want to (changing size
 one Unidata coordinate variables into size-one auxiliary coordinate
 variables or vice-versa). It is flexibility in the treatment of data which
 is of benefit to users of data.

 I appeal to you to consider this argument as a kind of compromise and to
 allow the clarification we propose to be made.

 Best wishes and thanks

 Jonathan

-- 
Ticket URL: <https://cf-pcmdi.llnl.gov/trac/ticket/104#comment:10>
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