Dear Roy
> Consider a case where a metadata record has two fields, one for geographic
> coverage and one for parameter. If selection drop-downs for these are
> covered by two separate lists - either vocabs or within an ontology - then
> 'sea_temperature' will not appear in the geographic coverage drop-down and
> 'Atlantic_Ocean' will not appear in the paramer drop-down. Were both
> drop-downs covered by a single ' Standard Name list' then both terms would
> appear. This not only increases the risk of field population with nonsense
> (the type of error I was visualising - admittedly it's still possible to
> call temperature salinity), but also makes the drop-down appear eccentric to
> say the least.
We distinguish between lists for (a) standard names (b) the possible values of
quantities which have a standard name. "atlantic_ocean" is not a standard name;
it is a possible value for a variable whose standard name is "region". A menu
of standard names would includes sea_surface_temperature, rainfall_flux,
latitude, region and land_cover (to list a few from the present table) and
also (if my proposal is agreed, to meet Paco's requirement) source, institution
and experiment_id. These are all names for things which a data variable or a
coordinate variable could contain. The *values* of these variables are dealt
with in other ways. sea_surface_temperature, rainfall_flux and latitude are
numeric, so no list is needed. The others are string-valued. At present only
region has standardised values; the possible values are given by
http://www.cgd.ucar.edu/cms/eaton/cf-metadata/region.html
It's quite likely we might develop a standard list for land_cover. As we have
discussed a lot, it would be useful to make links to other people's controlled
vocabularies if we can, and the proposal also includes a new attribute to point
to external lists of the possible values for a quantity (Bryan's suggestion).
> Jon's comment that we can carry on as we are now and change later worries me a little. So many times in my work with metadata I have found that aggregation is infinitely easier than teasing things apart.
It is right to be cautious, but I think this reasonable concern of yours is
that things should be sufficiently informative. I agree with you. That's why
we spend so much time making sure we know exactly what quantity is being
identified by a standard name, and why quantities with different physical
dimensions (units) have different standard names. In this case, I think we
are talking about a categorisation that can be introduced whenever we need it.
There are only 814 standard names at present, so it would not be a big job to
classify them in future, given a clear criterion for doing it - which is what
we lack, since we don't have a need for it (as far as I can see).
Cheers
Jonathan
Received on Fri Dec 29 2006 - 03:35:25 GMT
