Explainations of interface/serializations (what is required) (Was: Re: [QUANTITY] Data Model for Quantity v0.5

[David Berry]

Brian,
      One of the problems which people may have is that the items in your
list below do not include "Mappings" or "Frames". This illustrates one of
my concerns that the serialisations in the doc do not seem to describe the
same model as the interface. It seems like we have two models in the doc,
one defined by the interface and one implied by the example
serialisations. Why can we not have a serialisation in which (for
instance) a CoreQ contains a (Mapping or ValuesList) and a Frame:

   <CoreQ>
      <Mapping> (or <ValuesList>)
       ...
      </Mapping>
      <Frame>
      ...
      </Frame>
   </CoreQ>




> > Moreover it would be nice to have a clear statement
> > of which parts are mandatory and which ones are optionnal, at each level,
> > in clear english (understable by non-english mother spoker like me)
>
> 	This *is* in the document, but may not be clear. OK, I will take a stab at
> 	a summary:
>
>          Basic Quantity [id attribute optional]
>                  UCD  -   Optional
>                  CoordSystem - Optional
>                  Units - Optional (Defaults to "unitless")
>                  DataType - Optional (Defaults to "string of arbitrary length")
>                  Value - Required
>                  Accuracy - Optional
>
>          Core Quantity [id, size attributes optional]
>                  UCD - Optional
>                  CoordSystem - Optional
>                  Units - Required (But if absent in serialization it defaults to "unitless")
>                  DataType - Required (But if absent in serialization it defaults to "string of arbitrary length")
>                  Values - Required
>                  Accuracy - Optional
>
>          Std Quantity [id, size attributes optional]
>                  UCD - Optional
>                  CoordSystem - Optional
>                  Units - Required (But if absent in serialization it defaults to "unitless")
>                  DataType - Required (But if absent in serialization it defaults to "string of arbitrary length")
>                  AxesList (gives coordinate frames for accessing values in Q) - Optional
>                  Values - Required
>                  AltValues - Optional
>                  Accuracy - Optional
>

David

----------------------------------------------------------------------
Dr David S. Berry    (dsb at ast.man.ac.uk)

STARLINK project		 |	Centre for Astrophysics
(http://www.starlink.ac.uk/)	 |	University of Central Lancashire
Rutherford Appleton Laboratory	 |	PRESTON
DIDCOT				 |	United Kingdom
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