Re: [galeon] [WCS-2.0.swg] CF-netCDF standards initiatives

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Robin, Alexandre wrote:


Hi Steven,


[...snip...]
What I would like us to work on is a transition path from CF-NetCDF data repositories and OPeNDAP services to a SWE (including WCS) infrastructure. The approach of SWE is not to put these previous investments into question but rather adapt to it. Nobody already using NetCDF + OPeNDAP should have to replace them by SWE equivalents. We should instead keep working on providing the SWE connectors to the NetCDF infrastructure already in place, and in the process make sure that SWE retains all the strength of the existing systems while allowing it to be even more accessible. 


Hi Alexander,
Thanks for the detailed, thoughtful response. As is so often the case, we're probably closer in our evaluations of the issues than it may have appeared. There is endless room for discussion about various legacy formats and whether they ought to be candidates for OGC standardization. I'll avoid going down that road. No one is advocating "bringing in everything". Rather we are debating the merits of brining in a particular technology (netCDF) that is of proven excellence. (Can we define the threshold of excellence for brining in a new technology? A good question -- also discussed in several other emails of this thread. At this point that threshold is merely implicit in the standards process -- i.e. is there a sufficient ground swell of support.)
In the preceding paragraph you have hit upon the theme that I, too, would want to carry forward as the essence of interoperability. It is echoed in Bryan's email today: 

   Bryan: 'The key thing folks need to remember about interoperability is that it really 
means "I want to do what I've always done with my data ... but with YOUR data (and 
services)" so _*it's all about devising interfaces*_.'
For tactical reasons (the completeness of existing documents, etc.) Ben has argued that the initial push in netCDF standardization in OGC should be on the binary data format. Tactical considerations are important; I am not wishing to reopen that question. But a number of us have argued that the target that is of central interest for purposes of interoperability is the NetCDF API and data model, rather than the binary data format. It is precisely this sort of API that is absent in the current OGC offerings. (As Bryan notes it is also next to impossible to develop as long as key semantics lie in semi-standardized, often divergent application schema.) It is through the API that the netCDF standard has gained traction -- enabling client reference libraries to be built and speeding along the development of client software. As you say (your next paragraph) this is fertile ground for blending netCDF and other OGC technologies. With the proposal to bring netCDF under OGC we are also advocating that this effort may yield significant benefits for the larger community of geospatial users who want to seriously work with 3d, time-dependent fluid earth science data. (Mind you, I would fully acknowledge that the netCDF API is a radical departure in direction from, say, the SOS specification. But here is where we need to become conservatives and realists in the standards process. The proper task for a standards committee is to codify and incrementally improve proven practices. Only in narrowly defined contexts is it likely to succeed at exploring next-generation technologies. NetCDF is the proven technology known to foster interoperability in its area of "suitability for purpose" (a nod to John, G.) -- particularly in combination with DAP. We know with some confidence that it deserves a higher level of de jure recognition. It is SWE Common that is the new experiment in this regard -- also well worth pursuing as long as we maintain an appropriate level of skepticism.)
One contribution I personally have in mind is to provide read/write support for SWE Common in existing NetCDF libraries. This way you would not even have to change anything about user habits (at least those casual users who never look inside the NetCDF file itself). They would still be able to open these files in the same software they have been using until know. Just the underlying format will have changed, just like in a new version of NetCDF...
That is a worthy plan. It is a plan that is further advanced by bringing the netCDF API inside the OGC family. 

   - Steve



Regards,


-------------------------------------------------

**Alexandre Robin**

Spot Image, Web and E-Business

Tel: +33 (0)5 62 19 43 62

Fax: +33 (0)5 62 19 43 43

http://www.spotimage.com

Before printing, think about the environment


------------------------------------------------------------------------

*De :* Steve Hankin [mailto:Steven.C.Hankin@xxxxxxxx]
*Envoyé :* lundi 24 août 2009 19:42
*À :* Robin, Alexandre
*Cc :* Tom Whittaker; Ben Domenico; Unidata GALEON; wcs-2.0.swg
*Objet :* Re: [galeon] [WCS-2.0.swg] CF-netCDF standards initiatives




Robin, Alexandre wrote:

Hi Steve,
I agree that the target of OGC is not necessarily the "development of a single, definitive standard ».
However the other extreme position of "bringing everything in and letting the market decide" obviously leads to lack of interoperability, especially across communities... 

Hi Robin,
This use of hyperbole -- "100% overlap" and "bringing in everything" -- is leading to confusion. We're not talking about "bringing in everything". We're talking about bringing in a highly effective, modern, well-supported, open technology that has a large, dedicated community of data suppliers, application developers and users. NetCDF (& associated tooling) is arguably emerging as the definitive standard for interchange of 3-dimensional, time-dependent fluid earth system datasets.
I would like to point out that yes KML came in OGC although overlapping with GML, but that ESRI binary shapefile format did not. Perhaps OGC was more pure at the time...
I would certainly hope that the use of shapefiles was seriously discussed before being rejected for sound, substantive reasons. Purity is not a sound, substantive reason. Interoperability is the goal. Interoperability requires data interchange techniques that have been demonstrated to provide the functionalities that communities need. It also requires years of hard work at building up data repositories, applications, and user habits. These represent large financial investments in the technology. The netCDF tools and associated community will bring immense value into OGC. If we as spec designers don't start rationalizing among these many possibilities, then who will?
I hope there will be a rethinking of this perception of what it means to be "spec designers". You can write meaningful specs to describe a product that has already been developed and tested under realistic demands. That activity can be the foundation of a high quality standard. However, writing so-called "specs" for technologies that have yet to be properly tested is self-defeating in the end. Too often those activities are attempts at innovation. It is a trap that standards committees need to be on the alert against.
Wouldn't you gain in getting more active in OGC standard groups that try to address the same issues as NetCDF before making up your mind??
Time permitting, the answer is that we all need to be maximally aware of alternative solutions -- both inside of OGC standards groups and outside. I'm afraid that time is a barrier, though. If there is a community that has developed a SWE Common approach to the point that it can demonstrate a realistic ability to replace netCDF, it is incumbent upon you to advertise the evidence for this. We cannot all join OGC committees. (I put in my years on a standards committee long ago.) And this question can equally be turned the other way: OGC standards groups need to be sure to survey proven, existing technologies (particularly open technologies) and assess their merits (not their "purity") before designing new solutions. 

    - Steve


Regards,


-------------------------------------------------

**Alexandre Robin**

Spot Image, Web and E-Business

Tel: +33 (0)5 62 19 43 62

Fax: +33 (0)5 62 19 43 43

http://www.spotimage.com

Before printing, think about the environment


------------------------------------------------------------------------

*De :* Steve Hankin [mailto:Steven.C.Hankin@xxxxxxxx]
*Envoyé :* vendredi 21 août 2009 20:02
*À :* Robin, Alexandre
*Cc :* Tom Whittaker; Ben Domenico; Unidata GALEON; wcs-2.0.swg
*Objet :* Re: [galeon] [WCS-2.0.swg] CF-netCDF standards initiatives




Robin, Alexandre wrote:

Hi Steve,
Just to clarify when I said NetCDF was a "NEW standard" I meant a new standard in OGC.
As I was telling Ben in an offline email, I am totally conscious of its penetration and usefulness in certain communities.
However, _I am not convinced that /having two standards doing the same thing in OGC /is sending the right message and is the best way to go for a standardization organization_. 

Hi Robin,
I confess that I was aware of using a cheap rhetorical device when I twisted your intended meaning of "NEW". (Begging your tolerance.) It was helpful in order to raise more fundamental questions. You have alluded to a key question just above. Is it really best to think of the target of OGC as a the development of a single, definitive standard? one that is more general and more powerful than all existing standards? Or is it better to think of OGC as a process, through which the forces of divergence in geospatial IT systems can be weakened leading towards convergence over time? The notion that there can be a single OGC solution is already patently an illusion. Which one would you pick? WFS? WCS? SOS with SWE Common? SOS with its many other XML schema? (Lets not even look into the profusion of WFS application schema.) I trust that we are not pinning our hopes on a future consolidation of all of these. There is little evidence to indicate that we can sustain the focus necessary to traverse that path. The underlying technology is not standing still.
What Ben (and David Arctur and others) have proposed through seeking to put an OGC stamp of approval on netCDF-CF technology is similar to what OGC has achieved through putting its stamp on KML ("There are sound business and policy reasons for doing so.") It is to create a process -- a technical conversation if you will -- which will lead to interoperability pathways that bridge technologies and communities. Real-world interoperability.
There has been a lot of experimentation with SWE technologies as well that you may not know about and in many communities, especially in earth science.
What I'm saying is that perhaps it is worth testing bridging NetCDF to SWE before we go the way of stamping two 100% overlapping standards as OGC compliant.
Complete agreement that this sort of testing ought to occur. And interest to hear more about what has been achieved. But great skepticism that there is this degree of overlap between the approaches. And disagreement that this testing ought to be a precondition to OGC recognition of a significant ,community-proven interoperability mechanism like netCDF. OGC standardization of netCDF will provide a forum for testing and experimentation to occur much more rapidly and for a 2-way transfer of the best ideas between approaches. NetCDF & co. (its API, data model, CF, DAP) have a great deal to offer to OGC. 

    - Steve



Regards,


-------------------------------------------------

**Alexandre Robin**

Spot Image, Web and E-Business

Tel: +33 (0)5 62 19 43 62

Fax: +33 (0)5 62 19 43 43

http://www.spotimage.com

Before printing, think about the environment


------------------------------------------------------------------------

*De :* Steve Hankin [mailto:Steven.C.Hankin@xxxxxxxx]
*Envoyé :* jeudi 20 août 2009 20:58
*À :* Tom Whittaker
*Cc :* Robin, Alexandre; Ben Domenico; Unidata GALEON; wcs-2.0.swg
*Objet :* Re: [galeon] [WCS-2.0.swg] CF-netCDF standards initiatives


Hi Tom,
I am grateful to you for opening the door to comments "from 10 thousand feet" -- fundamental truths that we know from many years of experience, but that we fear may be getting short shrift in discussions of a new technology. I'd like to offer a comment of that sort regarding the interplay of ideas today between Robin ("/I hope we don't have to define a NEW standard .../") and Carl Reed ("/there are other organizations interested in bringing legacy spatial encodings into the OGC. There are sound business and policy reasons for doing so./").
The NEW standard in this discussion is arguably SWE, rather than netCDF. NetCDF has decades of practice behind it; huge bodies of data based upon it; a wide range of applications capable of accessing it (both locally and remotely); and communities that depend vitally upon it. As Ben points out, netCDF also has its own de jure pedigree. A key peril shared by most IT standards committees -- a lesson that has been learned, forgotten, relearned and forgotten again so many times that it is clearly an issue of basic human behavior -- is that they will try to innovate. Too-common committee behavior is to propose, discuss and document new and intriguing technologies, and then advance those documents through a de jure standards process, despite an insufficient level of testing. The OGC testbed process exists to address this, but we see continually how large the gap is between the testbed process and the pace and complexity of innovations emerging from committees.
Excellent reading on this subject is the essay by Michi Henning, /The Rise and Fall of CORBA/ (2006 -- http://queue.acm.org/detail.cfm?id=1142044). Among the many insights he offers is
**'Standards consortia need iron-clad rules to ensure that they standardize existing best practice.** There is no room for innovation in standards_._ Throwing in "just that extra little feature" inevitably causes unforeseen technical problems, despite the best intentions.'
While it adds weight to an argument to be able to quote from an in-print source, this is a self-evident truth. We need only reflect on the recent history of IT. What we need is to work together to find ways to prevent ourselves from continually forgetting it.
There is little question in my mind that putting an OGC stamp of approval on netCDF is a win-win process -- for the met/ocean/climate community and for the broader geospatial community. It will be a path to greater interoperability in the long run and it deserves to go forward. The merits of SWE (or GML) as an alternative approach to the same functionality also deserve to be explored and tested in situations of realistic complexity. But this exploration should be understood initially as a process of R&D -- a required step before a "standards process" is considered. If that exploration has already been done it should be widely disseminated, discussed and evaluated. 

    - Steve

==================================

Tom Whittaker wrote:

I may be ignorant about these issues, so please forgive me if I am
completely out-of-line....but when I looked at the examples, I got
very concerned since the metadata needed to interpret the data values
in the "data files" is apparently not actually in the file, but
somewhere else.  We've been here before:  One of the single biggest
mistakes that the meteorological community made in defining a
distribution format for realtime, streaming data was BUFR -- because
the "tables" needed to interpret the contents of the files are
somewhere else....and sometimes, end users cannot find them!
NetCDF and ncML maintain the essential metadata within the files: 
types, units, coordinates -- and I strongly urge you (or whomever) not
to make the  "BUFR mistake" again -- put the metadata into the files!
Do not require the end user to have to have an internet connection to
simply "read" the data....many people download the files and then
"take them along" when traveling, for example.
If I simply downloaded the file at 
<http://schemas.opengis.net/om/1.0.0/examples/weatherObservation.xml>
I would not be able to read it.  In fact, it looks like even if I also
got the "metadata" file at:
<http://schemas.opengis.net/om/1.0.0/examples/weatherRecord1.xml>
I would still not be able to read it, since it also refers to other
servers in the universe to obtain essential metadata.
That is my 2 cents worth....and I hope I am wrong about what I saw in 
the examples....
tom
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