[CF-metadata] Use of Standard Names and Coordinate Variables (relevant to the aerosol discussion)

From: Jonathan Gregory <j.m.gregory>
Date: Wed, 27 Sep 2006 16:03:54 +0100

Dear Bryan

Actually I agree with you. This is quite ironic, because my preference is
generally to put as much as possible in one attribute with as little hierarchy
as we can get away with, because it makes searching easier, and it means that
decisions about how to structure a hierarchy (which are generally hard and
often cause problems later, since any choice is arbitrary) can be avoided.
However in previous discussions I have felt myself to be a minority in arguing
against splitting up names. For instance, I think that special surfaces
(surface, TOA, tropopause, etc.) should be in the standard name, because there
are not many of them, and it would only make things more complicated to split
them off into a separate attribute.

I feel that parts of the description should appears as coordinates if there
are many possible values they could take, to avoid the vocabulary expanding
too much. If aerosol size can only foreseeably take a very small number of
values, it doesn't need to be a coordinate. On the other hand, we have provided
ways to make land surface type a coordinate, since it can take a lot of values
and every type has the same kind of quantities which need to be named. More-
over, in that case the answer to
> Do we ever expect people to use these variables as coordinates per se?
is Yes. Land surface type is a coordinate (a tile index) in models.

> I'm not even convinced by the argument that wavelength and
> RH should disappear off into coordinate variables either.
It depends principally on whether there are many possible values, I think.
Of course, if there is only possible value, it does not even need to be stated
in the standard name. It can just be part of the definition. The fact of
wanting to state it in the name itself implies that other values are possible.

Cheers

Jonathan
Received on Wed Sep 27 2006 - 09:03:54 BST