[GO-ESSP] Proposed netCDF attribute convention fordataset discovery

Bryan Lawrence b.n.lawrence at rl.ac.uk
Wed Sep 21 10:29:09 MDT 2005


Hi Ethan

> >I only have one tiny reservation with the syntax, and that's where you use
> > a controlled vocab, I think you should indicate the domain first then the
> > vocab. So, for cdm_data_type, I think it would be better to make it
> > cdm_domain: data type namespace
> >cdm_data_type: from the namespace enumeration
>
> There are three places we do this kind of thing.
> 1) "keywords" and "keywords_vocabulary"
> 2) "standard_name" and "standard_name_vocabulary"
> 3) "cdm_data_type" and "cdm_domain" (OR maybe "data_type" and
> "data_type_domain")
>
> First off, I like the use of "domain" better than "vocabulary", I think
> I'll switch to that with keywords and standard names.
> Second, any thoughts on how/if to allow the use of keywords or standard
> names from multiple domains?
> Third, any thoughts on enumerating the domains? (I.e., it would be great
> if everyone used the same domain ID to indicate a given domain.)

One way for handling this would be to borrow from the namespace prefix 
structure of xmlschema. One could simply declare the namespaces of domains, 
and then qualify the keywords.

> The "cdm" in "cdm_data_type" stands for the Common Data Model. So, that
> is the domain we were targeting though the enumeration is actually
> defined in the THREDDS catalog spec. Generalizing to "data_type_domain"
> would open it up to CSML feature types and such. So, I'll change these
> to "datatype" and "datatype_domain".

e.g ... leaving aside the syntax, semantically we could define
domain http://standard_url/common_data_model cdm
domain http://ndg.nerc.ac.uk/schema/csml_features csml
and have
datatype cdm:station etc
datatype csml:grid etc

i.e. use a uri (not necessarily a url*) as an identifier which defines the 
namespace in a unique way, and then a prefix to qualify any datatypes. 
One could even ommit the prefix if only one domain was specified.

* i.e. there doesn't have to be anything living at the url, but that should 
uniquely define a domain and the owner of that domain would be responsible 
for that controlled vocab/domain (me, I don't think there is much difference 
between what I mean by vocab and you mean by domain, so I'm not fussed, for 
us a vocab is more than just words, it'll lead naturally to feature types 
which is what I think you mean by domain).

As far as the metadata authorship goes, I take your point about separating the 
dataset authorship from the metadata authorship, and you're only 
concentrating on the former ... 

Cheers
Bryan

-- 
Bryan Lawrence
Head, NCAS/British Atmospheric Data Centre
Director, CCLRC/Environmental Data Archival and Associated Research
badc.nerc.ac.uk, home.badc.rl.ac.uk/lawrence, +44 1235 445012
(CCLRC, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX)


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