Hi Ben,
that appears to be an excellent summary! Let me underline, from a WCS viewpoint,
that we are most happy if these coverage encoding formats are not tightly
coupled with WCS - by making each encoding self-contained, coverages can float
between different services while retaining their clear, interoperable shape. A
win for all I believe.
OWS Common makes a lot of sense to me, but: we do not have a SWG for it -
actually, despite flaws of 2.0 are painfully known nobody has been speaking up
as a savior for quite some time. Would someone take on this change of OWS
Common? That makes him or her the Hero of the Day for me!
my 2cents,
Peter
On 03/26/2013 06:59 PM, Ben Domenico wrote:
Hi all,
The Coverages DWG, the WCS SWG, and the CF-netCDF SWG had several "lively" and
hopefull productive discussions regarding how to incorporate coverage
encodings (e.g., geoTIFF, JPEG2000, netCDF) into OGC protocol specs (not just
WCS but also possibly WFS, SOS, WPS, ...). There appears to be general
agreement that, as much as possible, these coverage encoding specifications
(e.g., the encoding data model mappings to GMLCOV and the special parameters
for each binary encoding) should be decoupled from the data access protocols.
If you recall, we had been proposing the CF-netCDF specifically as an
encoding for WCS 2.0.
So far several ideas have been proposed for how to go about doing this but,
as yet, there is no clear agreed-upon path. During these discussions, it was
noted that the OGC Architecture Board is also considering ways to streamline
and simplify some of the rather rigid requirements for how the specification
documents are written. Some possible mechanisms are aiming for breaking specs
into fewer modules, providing a cleaner and less distracting means for dealing
with HTTP URI requirements of the OGC Naming Authority, and perhaps less
emphasis and dependence on UML diagrams. Having spent a large fraction of my
time writing and rewriting those portions of the existing CF-netCDF documents,
I think these are moves in the right direction.
On the other hand, we needed to get the remaining specs relating to CF-netCDF
adopted by OGC. After a discussion with Stefano (who was not at the OGC
meetings) last Friday, we came up with the following:
An avenue that seems promising is to take the document that has been created
as a WCS extension for CF-netCDF encoding and rewrite it as an encoding
specification extension to OWS Common. The chapters that describe the
mapping between CF-netCDF and GMLCOV would remain pretty much the same.
However the requirements that pertain to the WCS (2 from chapter 6 and the
remainder in chapter 7) would be rewritten to refer to OWS Common instead of
WCS. The specification would thus have two conformance classes: one for the
GMLCOV mapping and one for the OWS Common connection. Using OWS Common would
ensure the encoding would be decoupled from any one OGC protocol so it could
be used by any of them. I believe housing such specs that apply to all the
protocols is one of the primary reasons for the existence of OWS Common.
My understanding is that this specification could be proposed by any SWG so we
might consider proposing it in the CF-netCDF SWG instead of WCS. On the
other hand, for a case like geoTIFF where there is no OGC SWG, it could be
proposed by the WCS SWG. The point is that A SWG proposes the specification
the TC. From our discussion at last week's TC, I understood the conclusion
to be that, if the TC votes it in as an OGC standard, it does not matter which
SWG initiated it.
Our struggle in the TC discussions was to determine a logical place for such
specification documents to reside. OWS Common seems to be such a logical place.
As usual, these OGC specification requirement issues are difficult to
summarize concisely and clearly, but I hope this note provides an
understanding of the fundamental questions and a possible way forward for
CF-netCDF.
-- Ben
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Dr. Peter Baumann
- Professor of Computer Science, Jacobs University Bremen
www.faculty.jacobs-university.de/pbaumann
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