Hi Roy,
I would strongly echo your perception of URNs as "interoperability
bridges". I think (hope?) the day will come when all of the _standard_
CRS information associated with a netCDF variable will be referenced via
a single URN-type attribute, e.g.
float temp(lat,lon):
temp:crs_id = "urn:ogc:def:crs:EPSG:6.3:4326" // OGC-defined URN
for WGS 1984 CRS.
Clearly it doesn't make sense to repeatedly specify low-level CRS
information in thousands of netCDF files. Such information has already
been offically defined by a recognised technical authority (currently
EPSG/OGP). We simply want to look up that definition at run-time
(whether locally or across the internet).
However, not all existing netCDF-aware client software is able to
understand these URNs. So until these applications have been upgraded,
or replaced in favour of more capable solutions, we need to support both
the human-readable and computer-readable methods of defining CRS (and
indeed other) properties. Presumably at some point URNs will become so
pervasive - and understood - that the long-form text definitions will
become deprecated and instead looked-up on demand. I see this process as
part of the interoperability bridge.
There have been criticisms - well-founded probably - that these new URNs
are verbose and abstruse. Maybe so, but I think that's just part of
learning a new set of terms. After all, terms like "WGS 84" and "NAD
1983" could be considered similarly abstruse, yet they are probably well
known in the earth science community simply because of their frequent
use. URNs will, I believe, become familiar in a similar fashion.
Moreover, well-designed software clients should hide much of this detail
from general end-users.
Regards,
--Phil
> Hello Jonathan,
>
> I've shifted off Trac onto the list because I feel that this is
> developing into a separate thread and didn't want to divert the
> coordinates debate off track. What we gain by including URNs is the
> ability to use tools that know about netCDF and the URN standard but
> not about CF. I'm thinking about areas other than CRS here - such as
> labelling parameters with a URN leading into an ontology. I guess
> where our viewpoints differ is that I am continually concerned with
> establishing interoperability, particularly semantic interoperability,
> between CF and other standards, whereas you have a more self-contained
> view of CF. From my position I see URNs as interoperability bridges
> whereas you see then as unecessary redundancy.
<snip>
>
> Cheers, Roy.
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