[CF-metadata] Encoding Errors on variables in CF

[Bryan Lawrence]

Hi Jonathan

> variables. However, I am not convinced about introducing a linking
> attribute, because I don't think the relation is so close that it needs to
> be given this special status. 

ok, I can accept that argument but ... see below

> In this particular case, you can look for another variable with the same
> spatiotemporal metadata and a standard_name which contains the original one
> as a pattern. That would be very general. 

... but I had got the thought from the previous emails that we didn't want to 
enforce "error" into standard names ... and I think it would introduce a new 
problem:

My radiosonde example is still a good one, and it's real: 

For each measurement in a profile I have a number which is an error (which 
might be a physical error quantity but is more likely a percentage). So, for 
an individual radisonde profile, say of humidity, then I have the 
measurement, and an error (let's say a percentage, which increases with 
height). So, I can see that I could have two variables in the file which are 
the humidity and the error (percentage). 

I could then produce a climatology from a year's measurements, and now the 
error of interest is the standard error associated with the variance between 
measurements within the month and it has rather different units than the 
error did in the previous case, still with the same names for the variables 
if we were trying to introduce an error standard name for every standard name 
... (have i misundestood this point?).

The key point here is that different communties have rather different idea of 
what we mean by an error ... even with the same source data ... albeit at 
different stages of maturity.

I would have thought it would have been cleaner to have an optional link 
between two variables ... software could simply fail gracefully if the link 
was broken.   This is nothing more than a "data hyperlink" ...

... but I dont feel strongly about this, as long as we can find a sensible way 
of doing it ...

Bryan

-- 
Bryan Lawrence, Head NCAS/British Atmospheric Data Centre
web: www.badc.nerc.ac.uk  phone: +44 1235 445012
CLRC: Rutherford Appleton Laboratory, Chilton, Didcot, OX110QX, UK