[CF-metadata] quantities requiring parameters to define them

From: Jonathan Gregory <j.m.gregory>
Date: Mon, 25 Oct 2004 08:55:38 +0100

Dear Derrick

> This could be solved but next, we'll see neutral
> density (commonly called gamma) which is defined with respect to an
> independent set of 3d data, not just a formula.

In a similar way, formula_terms can point to a 2D field of pressure data in
order to calculate p from a sigma coordinate variable. However, a standard
name modifier could also indicate a field of data. Either mechanism could be
used in practice. Neither is exactly analogous to what we need, which is to
record parameters (global or a function of independent coordinates) that are
needed to define the quantity in the variable. By contrast, standard name
modifiers supply metadata about the values of the variable, while formula terms
supply parameters needed to compute other quantities from the values in the
variable.

I think I prefer formula_terms because formula_terms are defined explicitly
for each standard name i.e. what terms it can have and what they mean. By
contrast, standard name modifiers are defined in a way which is not specific to
the standard names with which they might be used. Hence I think that with
formula_terms it will be easier to make the dataset more self-describing,
unless we substantially depart from what I understood as the intention of
standard name modifiers. In answer to

> where is the practical division between relying on a
> user's intuition or knowledge and creating "fully self describing" data sets?

I think we should rely as little as possible on intuition.

Cheers

Jonathan
Received on Mon Oct 25 2004 - 01:55:38 BST