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#95: Development of CF 1.5 Data Model
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  Reporter:  markh           |       Owner:  [email protected]
      Type:  task            |      Status:  new                          
  Priority:  medium          |   Milestone:                               
 Component:  cf-conventions  |     Version:                               
Resolution:                  |    Keywords:                               
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Comment (by markh):

 In trying to describe the two coordinate constructs, I have been
 considering roles and characteristics, and pondering the comments made to
 date.

 It appear to me we have two characteristics here and two roles.  The
 management of the role seems to me to sit firmly with the Field, whilst
 the characteristic is in the nature of the coordinate the Field
 references.  The language used to describe this is not delivering this
 message for me.

 I wonder whether we would improve the model by recognising that the
 'dimension' or 'auxiliary' nature of the coordinate is defined by the
 Field while the coordinate characteristics are the responsibility of the
 coordinate to define.  I think this division of responsibility could bring
 clarity to the model.

 This leads me to suggest an alteration to the descriptions of the
 assocations.

  * A Field will declare:
   * dim_coordinates: a set of containment associations, each mediated by
 one and only one explicit domain axis.
   * aux_coordinates: a set of containment associations, each mediated by a
 collection of domain axes (recognising the constraints on shape matching).

 This, in turn, leads me to think that we may have our names wrong for our
 constructs.  The coordinate types are not dimension and auxiliary, they
 are ordered and unordered.

 An !OrderedCoord is a coordinate instance which asserts that it has an
 explicitly defined order: it is sortable, monatonic and 1-dimensional.

 An !UnorderedCoord is a coordinate instance which does not assert that it
 has an expliucitly defined order.

 The only constraint required on the Field is that the dim_coordinates
 association may only contain !OrderedCoord references.

-- 
Ticket URL: <https://cf-pcmdi.llnl.gov/trac/ticket/95#comment:24>
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