Thanks for getting this rolling again. I have been meaning to reply, just been
tied up with other things. Interesting to look at what has been tried, and
also people's experience with how much server-side functions can be done
synchronously without any limit on the amount of resources the request might
consume.
-Roy
On Jun 28, 2012, at 12:12 PM, Dennis Heimbigner wrote:
> Roy has raised the issue (my paraphrase) of the form that a
> URL should take to initiate a server-side computation.
>
> Let me propose as a starting point the following approach,
> which I had experimented with recently.
>
> =Dennis Heimbigner
> Unidata
>
>
> Server-Side Expression Proposal
> -------------------------------
>
> A semantically nonsensical, but syntactically correct, example might
> look something like this.
>
> $x=f("string17",g(h(12))),f2($x,p[0:3:10])
>
> The idea is that a URL would contain in its query section
> (the part after the '?') a set of comma separated expressions.
> An expression would be either
> 1. a function invocation, or
> 2. an assignment of a function invocation to
> a single-assignment variable.
>
> A function invocation is your typical one of the form
> f(arg1,arg2,...,argn)
> where the arguments can be any of the following.
> 1. another, nested, function invocation
> 2. a constant (string, number, etc)
> 3. a dataset
> 4. a variable.
>
> The value of a function is a dataset (see below) so that
> functions can be nested/composed.
>
> The term "dataset" is intended to cover all of the following
> possibilities.
> 1. whole dataset (e.g. a DAP Dataset or a netcdf dataset)
> 2. a variable within a dataset (variable here is not be confused
> with a single-assignment variable.
> 3. a range expression applied to a variable within a dataset
> p[0:1:30], for example.
>
> The term "single-assignment" means that a variable can have
> a value assigned to it exactly once. The reason for using
> single-assignment is that allows for the representation of
> any possible data-flow without introducting the notion of
> mutable state.
>
> The above is just a sketch, and there are many details
> I am ignoring (such as typing and namespaces).
>
> =Dennis Heimbigner
> Unidata
>
>
> Roy Mendelssohn wrote:
>> Hi All:
>> Ah, as usual I get to be the wet blanket. I am not as excited about WPS, or
>> for that matter most OGC standards, as others, because I find since OGC
>> tries to answer the general question, the resultant services have to deal
>> with the most complex case, therefore the 80% of uses cases that aren't that
>> complex are burdened with overly complex services, that are difficult for
>> the average user, and require constant update of software, and software that
>> is hard to embed into existing applications.
>> Most of what a lot of us do are essentially read-only services. For these,
>> I much prefer the basic approach presently used by F-TDS and GDS, though
>> there can be discussion of how best to connote an expression, and what the
>> syntax should be. Even more, as has been noted, WPS does not solve the key
>> question of the syntax of the expressions.
>> So I know this will start a lot of flames, but I just look at the service
>> that we developed and use, ERDDAP. All sorts of people, who only know a
>> little programming, successful use ERRDAP in R, Matlab, shell scripts,
>> python, java etc., and it is easy to use from within applications, because
>> any environment that can send a URL and receive a file can use it.
>> Moreover, since only methods internal to the applications are used, the
>> scripts or programs or whatever do not break as both the application and
>> operating environment change.
>> Our experience over many years of serving data is that in most cases, simple
>> and fast are to be preferred. Clearly people can come up with counter cases
>> that are not covered, and I am all for developing services for those cases,
>> but not for burdening simpler cases with all that baggage.
>> My $0.02.
>> -Roy
>> On Jun 19, 2012, at 12:14 AM, <stephen.pascoe@xxxxxxxxxx> wrote:
>>> We are working on wrapping CDO operators in our WPS implementation
>>> COWS-WPS. This work is being done as part of the IS-ENES an ExArch projects
>>> with with DKRZ, KNMI and others.
>>> WPS doesn't define your functions for you but gives you a protocol and
>>> framework for asynchronous server-side tasks.
>>> http://cows.ceda.ac.uk/cows_wps/intro.html
>>>
>>> --
>>> Stephen Pascoe from iPhone
>>>
>>> On 18 Jun 2012, at 23:07, "John Cartwright" <john.c.cartwright@xxxxxxxx>
>>> wrote:
>>>
>>>> Could the the OGC's Web Processing Service spec
>>>> (http://en.wikipedia.org/wiki/Web_Processing_Service) serve that
>>>> function?
>>>>
>>>> --john
>>>>
>>>>
>>>> On Mon, Jun 18, 2012 at 3:56 PM, Roy Mendelssohn
>>>> <roy.mendelssohn@xxxxxxxx> wrote:
>>>>> But for a useful service, the form and syntax of the URL should be
>>>>> independent of the mechanism that does the server side calculations
>>>>> (which rules out SWAMP). So for example, both Grads an F-TDS use the
>>>>> same format in the URL to say that "this is an expression", but the
>>>>> expressions themselves are platform specific. That is not the way to get
>>>>> overarching services.
>>>>>
>>>>> Instead, we need agreement on how in the URL request we signal a
>>>>> server-side function, the syntax of that function (independent of the
>>>>> engine underneath) and a few simple functions to start (say simple data
>>>>> transformations, differencing and averaging on a dimension(s)). Then the
>>>>> server back-end can parse the request and use Ferret or Grads or NCO or
>>>>> Python or whatever is desired, and like with any good service, the back
>>>>> end could change without having any affect on the URL or the user.
>>>>>
>>>>> I know Matthew Arrott at least used to like the approach in Chapter 12 of
>>>>> "Python Scripting for Computation Science". But a lot of that is the
>>>>> engine underneath. I am more interested in the form of the URL. Get
>>>>> some agreement on that, and some real implementation could proceed.
>>>>>
>>>>> -Roy
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> On Jun 18, 2012, at 2:37 PM, Russ Rew wrote:
>>>>>
>>>>>> Jeff,
>>>>>>
>>>>>>> However, we have to keep in mind performance ramifications. It still
>>>>>>> takes
>>>>>>> a long time to move gigabytes of data across a network. This brings up
>>>>>>> the
>>>>>>> importance of moving the computation to the data, instead of moving the
>>>>>>> data to the computation. For some data sets and many use cases remote
>>>>>>> access to data works very well so things like brokering are tractable.
>>>>>>> However, for *big* data sets (e.g., climate model output) we need to
>>>>>>> come
>>>>>>> up with richer mechanisms (like the NCO on local data) to bring
>>>>>>> computation
>>>>>>> to the data.
>>>>>> See Daniel Wang's SWAMP (the Script Workflow Analysis for
>>>>>> MultiProcessing), built on top of NCO:
>>>>>>
>>>>>> https://code.google.com/p/swamp/
>>>>>>
>>>>>> --Russ
>>>>>>
>>>>>> _______________________________________________
>>>>>> thredds mailing list
>>>>>> thredds@xxxxxxxxxxxxxxxx
>>>>>> For list information or to unsubscribe, visit:
>>>>>> http://www.unidata.ucar.edu/mailing_lists/
>>>>> **********************
>>>>> "The contents of this message do not reflect any position of the U.S.
>>>>> Government or NOAA."
>>>>> **********************
>>>>> Roy Mendelssohn
>>>>> Supervisory Operations Research Analyst
>>>>> NOAA/NMFS
>>>>> Environmental Research Division
>>>>> Southwest Fisheries Science Center
>>>>> 1352 Lighthouse Avenue
>>>>> Pacific Grove, CA 93950-2097
>>>>>
>>>>> e-mail: Roy.Mendelssohn@xxxxxxxx (Note new e-mail address)
>>>>> voice: (831)-648-9029
>>>>> fax: (831)-648-8440
>>>>> www: http://www.pfeg.noaa.gov/
>>>>>
>>>>> "Old age and treachery will overcome youth and skill."
>>>>> "From those who have been given much, much will be expected"
>>>>> "the arc of the moral universe is long, but it bends toward justice" -MLK
>>>>> Jr.
>>>>>
>>>>> _______________________________________________
>>>>> thredds mailing list
>>>>> thredds@xxxxxxxxxxxxxxxx
>>>>> For list information or to unsubscribe, visit:
>>>>> http://www.unidata.ucar.edu/mailing_lists/
>>>> _______________________________________________
>>>> thredds mailing list
>>>> thredds@xxxxxxxxxxxxxxxx
>>>> For list information or to unsubscribe, visit:
>>>> http://www.unidata.ucar.edu/mailing_lists/
>>> --
>>> Scanned by iCritical.
>>>
>>> _______________________________________________
>>> thredds mailing list
>>> thredds@xxxxxxxxxxxxxxxx
>>> For list information or to unsubscribe, visit:
>>> http://www.unidata.ucar.edu/mailing_lists/
>> **********************
>> "The contents of this message do not reflect any position of the U.S.
>> Government or NOAA."
>> **********************
>> Roy Mendelssohn
>> Supervisory Operations Research Analyst
>> NOAA/NMFS
>> Environmental Research Division
>> Southwest Fisheries Science Center
>> 1352 Lighthouse Avenue
>> Pacific Grove, CA 93950-2097
>> e-mail: Roy.Mendelssohn@xxxxxxxx (Note new e-mail address)
>> voice: (831)-648-9029
>> fax: (831)-648-8440
>> www: http://www.pfeg.noaa.gov/
>> "Old age and treachery will overcome youth and skill."
>> "From those who have been given much, much will be expected" "the arc of the
>> moral universe is long, but it bends toward justice" -MLK Jr.
>> _______________________________________________
>> thredds mailing list
>> thredds@xxxxxxxxxxxxxxxx
>> For list information or to unsubscribe, visit:
>> http://www.unidata.ucar.edu/mailing_lists/
**********************
"The contents of this message do not reflect any position of the U.S.
Government or NOAA."
**********************
Roy Mendelssohn
Supervisory Operations Research Analyst
NOAA/NMFS
Environmental Research Division
Southwest Fisheries Science Center
1352 Lighthouse Avenue
Pacific Grove, CA 93950-2097
e-mail: Roy.Mendelssohn@xxxxxxxx (Note new e-mail address)
voice: (831)-648-9029
fax: (831)-648-8440
www: http://www.pfeg.noaa.gov/
"Old age and treachery will overcome youth and skill."
"From those who have been given much, much will be expected"
"the arc of the moral universe is long, but it bends toward justice" -MLK Jr.
