[CF-metadata] URNs

[Philip Bentley]

Hi Seth

I don't think we should assume that a URN necessarily needs to be
resolvable (referenceable?) across the internet in order for a software
application to work with it. If an application 'understands' the meaning
of a particular URN then all's well.

It would be perfectly feasible for an organisation to maintain a local
cache of URNs, perhaps updated from the central authority on a periodic
basis. In a way, this is exactly what geospatial solutions such as ESRI
ArcGIS and Oracle Spatial do already. These products maintain copies of
the OGC CRS entities in local text files and/or rdbms tables. The CRS
entities are sufficiently slow-changing to make this a practical
solution.

Reductio ad absurdum, one could even hard-code URNs into a software
application that needs them, but I don't think this approach would find
many advocates!

Cheers

--Phil

On Wed, 2007-10-03 at 18:06 -0600, mcginnis at ucar.edu wrote:

> > I think that the description of the coord ref system in terms of projection,
> > ellipsoid and vertical datum can't be dispensed with until the day when it is
> > no more difficult to look it up on the net than it is to read it 
> > directly from
> > the file. Until then, the information has to be in the file to make the file
> > self-describing, and I would say that day is a long way off, when one 
> > considers
> > all the applications, some of them simple user-written programs, that want to
> > use the netCDF files.
> 
> 
> I think this is a really important point.
> 
> Consider that "just as easy to look it up on the net" implies not only 
> that users whose systems are not URN-aware can find out where to look 
> without much effort, but also that systems using NetCDF data have a net 
> connection that can quickly and reliably reach a server providing that 
> information.
> 
> A URN is great if you're sitting at your desk using a program that will 
> look it up for you.  If you're *writing* a program that does something 
> with the data, or if you're working someplace without easy internet 
> access, or if for some reason your net connection can't get to whatever 
> OGC site defines it, the URN may be no better than saying simply 'geoid 
> = "WGS 1984"'.  (Pity the hypothetical programmer working on code for 
> an autonomous submersible that talks to data-collection buoys...)
> 
> Cheers,
> 
> Seth
> 
> ----------------------------------------------------------------
> 
> 
> 
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