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Lorenzo, Firstly, it was nice to meeting you in real space. Hope your time in Reading is fruitful. I'm now back in Exeter. Secondly, Bryan, Ben, Dom, Jon, etc I have been watching the CF developments and the UncertML with some interest, but not enough time to keep track of the details. I thought some historical perspective may be of interest (alternatively, bin this!). When the WMO table driven data formats (GRIB, BUFR, CREX) were developed decades ago, the problems of uncertainty, statistical derivatives, and quality measures were recognised to be at odds with the concept of 'a single parameter space to rule them all' and introduced a completely new 'computable Turing space' to get lost in. We eventually introduced variable modifiers/operators that recognised this, after an initial single parameter space approach that put common statistical variants of parameters as equal citizens to the parameters themselves, providing there were examples in commmon use. This latter, pragmatic, approach also made things simpler and more compact - an overriding concern at the time, and still is. I suspect and hope that UncertML will allow a conceptually rigorous approach, but I would like three aspects to be considered and not excluded: a) The simple pragmatic approach that I mentioned. E.g. some observing instruments generate means and variances etc in a black box manner. Could these be accomodated without the heavyweight complexity of UncertML and the current CF approach? b) The current CF-NetCDF approach seems to be predicated on NWP models used in research communities, and it has not had much exposure to operational meteorology. The same applies to CSML. I would hope that the underlying conceptual models are robust enough to accomodate the operational scenarios and use cases. c) The WMO (operational) approach to quality is very much process orientated, and this is just different the current Inspire/ISO approach. I have attached a recent paper by Gil Ross on this. There may be a later version, but the relevant people are not around today. HTH, Chris Chris Little Co-Chair, OGC Meteorology & Oceanography Domain Working Group International Telecoms & Projects Met Office FitzRoy Road Exeter Devon EX1 3PB United Kingdom Tel: +44(0)1392 886278 Fax: +44(0)1392 885681 Mobile: +44(0)7753 880514 E-mail: chris.little@xxxxxxxxxxxxxxxx http://www.metoffice.gov.uk <http://www.metoffice.gov.uk/> ________________________________ From: cf-netcdf-1.0.swg-bounces+chris.little=metoffice.gov.uk@xxxxxxxxxxxxxxxxxxxxxxxx [mailto:cf-netcdf-1.0.swg-bounces+chris.little=metoffice.gov.uk@xxxxxxxxxxxxxxxxxxxxxxxx] On Behalf Of Lorenzo Bigagli Sent: 04 December 2011 18:00 To: Bryan Lawrence Cc: galeon@xxxxxxxxxxxxxxxx; CF-NetCDF-1.0.SWG@xxxxxxxxxxxxxxxxxxxxxxxx; Ben@xxxxxxxxxxxxxxxx Subject: Re: [CF-NetCDF-1.0.swg] [galeon] netCDF Uncertainty conventions(netCDF-U) Bryan, Dominic, all, I apologize for not following up sooner on your comments and questions. Please find enclosed the draft netCDF-U conventions, as presented to the Earth System Science DWG at the last OGC TC Meeting in Bruxelles last wednesday. The netCDF Working Group did not meet this time, so we would take the opportunity to continue the discussion on this mailing list, to address and incorporate your comments and improve the document for the next TC Meeting (march 2012, Austin, Texas). Your contribution is very welcome. We are also trying to engage the CF community (see the CF-metadata mailing list): I will ask them to express their interest in the topic, so we can keep them posted (possibly we can set up a dedicated mailing list, if need be). As you will read in the attachment, we have tried to be convention-neutral, in particular making sure that netCDF-U fully integrates with the netCDF-CF Conventions, using the same constructs when possible (e.g. the ancillary_variables attribute). Ideally, we think of datasets that would conform to both the conventions: :Conventions = "CF-1.5 UW-1.0" NetCDF-U is based on a generic mechanism for annotating netCDF variables according to the UncertML <http://www.uncertml.org/> conceptual model. The rationale for this it that we argue a probabilistic description of scientific quantities is a cross-cutting aspect that may be modularized. In particular, we wouldn't clutter the application-level dictionaries with probabilistic concepts and jargon. This said, I think the cell-methods mechanism has a partial overlapping with netCDF-U, in that it can account for (some of the) UncertML Summary Statistics concepts. However, it does not currently address Distributions and Samples. We could think of extending it, but we preferred to introduce a new mechanism, based on the standard URI syntax and RDF semantics. This is why we have represented the cell methods and measures just as strings in the UML. We agree that, although formally correct, this is a semantic approximation, however in our context we have overlooked their semantics, for the above reasons. On the other hand, the cell-methods mechanism is arguably more fine-grained than netCDF-U, allowing to express different methods on multi-dimensional variables, particular as far as the semantics of dimension intervals is concerned. I am unclear at the moment how much this is application dependent, and hence strictly pertaining to the CF conventions. In other words, it may be that some application would still need the more fine-grained semantics of CF cell-methods to make sense of the data. This is in line with our aim of netCDF-U being complementary to netCDF-CF, and not replacing it. On the other hand, a generic mechanism for associating distinct summary statistics semantics to distinct dimension variables may be useful in general. I am looking forward to discuss with you about this and I wait for any comments of yours. Regards, LB [see attached file: 11-163_NetCDF Uncertainty Conventions (netCDF-U) Discussion Paper.pdf] Il giorno 11/nov/2011, alle ore 15:15, Bryan Lawrence ha scritto: Hi Dominic, Lorenzo I note that the UML that appears in this is inaccurate as to CF around cell methods and measures as well, and perhaps getting that right might help. (One could model cell methods as an association class between a variable and a coordinate, or a specialisation of a variable, but it's certainly not a string ... likewise cell_measures are an enumeration attribute of the cell method). With those pieces in play wouldn't this proposal be much simpler? (I have to say that cell_methods are strictly associated with coordinates, rather than other variables, but I'd rather see the same fundamental mechanisms re-used, rather than new ones introduced). Cheers Bryan Hi Lorenzo, I am not sure whether I will be at the OGC meeting, but I am interested in how you see NetCDF-U Summary Statistics being compatible with existing CF Cell methods e.g. dimensions: time = UNLIMITED; // (5 currently) station = 10; nv = 2; variables: float pressure(station,time); pressure:long_name = "pressure"; pressure:units = "kPa"; pressure:cell_methods = "time: point"; float maxtemp(station,time); maxtemp:long_name = "temperature"; maxtemp:units = "K"; maxtemp:cell_methods = "time: maximum"; float ppn(station,time); ppn:long_name = "depth of water-equivalent precipitation"; ppn:units = "mm"; ppn:cell_methods = "time: sum"; double time(time); time:long_name = "time"; time:units = "h since 1998-4-19 6:0:0"; time:bounds = "time_bnds"; double time_bnds(time,nv); data: time = 0., 12., 24., 36., 48.; time_bnds = -12.,0., 0.,12., 12.,24., 24.,36., 36.,48.; http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.6/ch07s03.html It seems like UncertML references could perhaps be 'attached' to existing Cell method descriptions rather than being an alternative structure? Regards, Dom On 11 November 2011 12:06, <bigagli@xxxxxxxxxxx> wrote: Hi Stefano, all, it makes sense to me to present the NetCDF-U to the ESS DWG, since I'm already scheduled for a presentation on a germane topic. I don't think it's necessary to organize a meeting of the CDF-netCDF WG, if I'm the only presenter (thanks for your availability). I can certainly notify the MetOceans DWG: what other WGs should I inform, in your opinion? For the interested: the NetCDF draft Discussion Paper is posted to the pending documents of the OGC portal. Here is a direct link< https://portal.opengeospatial.org/files/?artifact_id=46702&version=1> (authentication required). Best regards, Lorenzo Il giorno 11/nov/2011, alle ore 11:42, Stefano Nativi ha scritto: Hi Ben and Lorenzo, I will be in Brussels on Tuesday morning and I'll co-chair the ESS meeting on Wednesday. I may organize a CF-netCDF meeting on Tuesday afternoon; however, Lorenzo could present the discussion paper in the ESS meeting -he is scheduled to give a short talk on the CF-netCDF importance for Earth system sciences. Stefano Hi Lorenzo, It's great that you've created a discussion paper on the uncertainty conventions. It is indeed an important topic. I will not be in Brussels for the TC there, so, if there is going to be a CF-netCDF session, someone else will have to organize it. Or you could present the topic in MetOceans or Earth Systems DWG. In any case, it is crucial that we move forward in this area. Thanks. -- Ben On Thu, Nov 10, 2011 at 11:38 AM, Lorenzo Bigagli <bigagli@xxxxxxxxxxx <mailto:bigagli@xxxxxxxxxxx>> wrote: Ben, all, this is to inform that I have uploaded to the pending documents a candidate Discussion Paper on the NetCDF Uncertainty Conventions (NetCDF-U) that we discussed in Boulder, for your possible review. I would like to (briefly) present it at the next TC Meeting in Bruxelles and to propose a motion for the TC to accept it as an OGC Discussion Paper. Your feedback is welcome. Regards, Lorenzo Bigagli --- Lorenzo Bigagli, Ph.D. National Research Council of Italy Institute of Methodologies for Environmental Analysis (CNR-IMAA) a: Area della Ricerca di Potenza, Contrada Santa Loja Zona Industriale, I-85050 Tito Scalo (PZ), Italy t: +39 0971 427221<tel:%2B39%200971%20427221> f: +39 0971 427222<tel:%2B39%200971%20427222> m: bigagli@xxxxxxxxxxx<mailto:bigagli@xxxxxxxxxxx> ________________________________ _______________________________________________ CF-NetCDF-1.0.swg mailing list CF-NetCDF-1.0.swg@xxxxxxxxxxxxxxxxxxxxxxxx<mailto: CF-NetCDF-1.0.swg@xxxxxxxxxxxxxxxxxxxxxxxx> https://lists.opengeospatial.org/mailman/listinfo/cf-netcdf-1.0.swg _______________________________________________ galeon mailing list galeon@xxxxxxxxxxxxxxxx<mailto:galeon@xxxxxxxxxxxxxxxx> For list information, to unsubscribe, visit: http://www.unidata.ucar.edu/mailing_lists/ -- Scanned by iCritical. -- Bryan Lawrence University of Reading: Professor of Weather and Climate Computing. National Centre for Atmospheric Science: Director of Models and Data. STFC: Director of the Centre for Environmental Data Archival. Ph: +44 118 3786507 or 1235 445012; Web:home.badc.rl.ac.uk/lawrence
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