Hi John,
Philosophically I am aligned with Bryan: the purpose of the CF standard
is to constrain (simplify and make predictable) the use of a highly
general file creation toolkit like netCDF. The question of limitations
placed on name strings should be evaluated on this yard stick.
There is a class of problems that are created by embedding special
syntax characters willy-nilly into name strings. Namely, that the use
of such characters can render mathematical expressions ambiguous.
Here's a simple example. Suppose a file contains 3 surface marine
variables -- lets say atmospheric CO2, ocean CO2 and an artfully
computed delta across the surface. Further say that the file creator
chooses to name the delta variable using a "-", as in
atmosCO2
waterCO2
and
// atmosCO2-waterCO2
Then the meaning of the mathematical expression "atmosCO2-waterCO2" has
been rendered ambiguous. Is it a single variable name, or the
difference of two? One is forced to use arbitrary tricks that are
alien to the scientific users we are trying to serve -- say
disambiguating the expression by insisting on surrounding quotes,
"atmosCO2"-"waterCO2", white space, "atmosCO2 - waterCO2". (Would any
scientist read "atmosCO2 - waterCO2" and "atmosCO2-waterCO2" to have
distinct meanings?)
As you say we have already headed down this (slippery) slope. Characters
like "+", "-", "." and case-sensitivity have leaked through into fairly
common practice. For better or worse. :-( (Should the publishers of
science textbooks start using case-sensitive variable names?) So the
question that you've posed is in a sense, /now that the horse is out of
the barn, is there any merit to keeping the other animals penned?/
Like Brian, I would argue that the way to answer this is to insist that
at least there be significant gains from letting them out.
Another unintended negative consequence: the impact on free text
searches when our variable names include special syntax characters.
Are our metadata procedures on an arc so promising that we have no need
to rely on general Google-style tools for discovery?
- Steve
=============================================
On 1/13/2014 12:12 PM, John Graybeal wrote:
> Not sure I am following you -- constraints are presumably there for a
> reason, I wasn't sure what the reason was for these particular
> constraints, but thought they might have simply echoed earlier netCDF
> constraints.
>
> To your 'use case' question, we were thinking about alternatives to
> mx_ as prefix for our own attributes, to minimize the chance of
> collisions (e.g., with some maintenance variables someone might name mx_).
>
> john
>
> On Jan 13, 2014, at 11:27, Bryan Lawrence <bryan.lawrence at ncas.ac.uk
> <mailto:bryan.lawrence at ncas.ac.uk>> wrote:
>
>> Hi John
>>
>> In the spirit of CF being *constrained* netCDF, it seems that we
>> wouldn't, unless we had a specific use case ... do you?
>>
>> Cheers
>> Bryan
>>
>>
>> On 13 January 2014 18:54, <john.graybeal at marinexplore.com
>> <mailto:john.graybeal at marinexplore.com>> wrote:
>>
>> As netCDF is growing to allow _at_, +, hyphen, and period in
>> variable/dimension/attribute names, is there any likelihood CF
>> will grow to allow some or all of those characters?
>>
>> I seem to recall some tools have conflicts with some of those
>> characters (aside from them being non-conformant). But
>> consistency and flexibility would be nice.
>>
>> john
>> ------------------------------------
>> John Graybeal
>> Sr. Data Manager, Metadata & Semantics
>>
>> M +1 408 675-5445 <tel:%2B1%20408%20675-5445>
>> skype: graybealski
>> Marinexplore
>> 920 Stewart Drive
>> Sunnyvale 94085
>> California, USA
>> www.marinexplore.com
>> <http://www.marinexplore.com/><http://marinexplore.com
>> <http://marinexplore.com/>>
>>
>>
>> --
>> Scanned by iCritical.
>>
>>
>>
>>
>> --
>>
>> Bryan Lawrence
>> University of Reading: Professor of Weather and Climate Computing.
>> National Centre for Atmospheric Science: Director of Models and Data.
>> STFC: Director of the Centre for Environmental Data Archival.
>> Ph: +44 118 3786507 or 1235 445012; Web:home.badc.rl.ac.uk/lawrence
>> <http://home.badc.rl.ac.uk/lawrence>
>
> ------------------------------------
> *John Graybeal*
> Sr. Data Manager, Metadata & Semantics
>
> M +1 408 675-5445
> skype: graybealski
> Marinexplore
> 920 Stewart Drive
> Sunnyvale 94085
> California, USA
> www.marinexplore.com <http://marinexplore.com>
>
>
>
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