Re: [wcsplus] asynchronous response [was: Re: WCS 1.0+]

Hi Ethan and all,

With Paolo we tried to expand this theme in order to come up with wider model and understand possible use cases. Starting from it, we tried to produce simple requirements to support most common use cases with WCS.

Hope could be useful.


P.S. I attached a Word document, let me know if you prefer a PDF version

Hi Stefano, all,

Yes, asynchronous response is part of WCS 1.0+ so I'm including your CR doc in this email.

John and I talked about asynchronous responses a bit the other day. Below are a few thoughts from our discussion (all of which are based in the REST/ROA realm rather than the SOAP/WS-* realm). I was going to suggest we continue this conversation but postpone implementation in WCS 1.0+ until later in the process. But with this CR being submitted, maybe it is worth moving forward sooner rather than later. Thoughts?

Use cases:
1) "Asynchronous Access" - The client wants the data stored for access in future step of chaining or some such. 2) "Asynchronous Response" - The server determines that it will take time to process and respond so wants to let client know to come back and get the data later.

Does anyone have more concrete use cases of the "Asynchronous Response" type? Jeremy, Bruce, this was on your list. What is(are) your use case(s)?

1) For the "Asynchronous Access" use case, I think the current way a WCS server lets the client know that it can "store" the data is fine (i.e., AllowedValues: "True", "False").

2) For the "Asynchronous Response" use case, the client needs 1) a way to know if the server might make an asynchronous response and 2) a way to indicate to the server that it wants a request fulfilled even if it is as an asynchronous response. Perhaps "AllowAsync". So the server indicates that it might do an asynchronous response by specifying the "AllowAsync" parameter with AllowedValues of "True" and "False", similar to the "store" parameter.

I'm guessing the WCS.RWG won't like the extra parameter as they seem to lean towards simplicity by reduction of parameters. But I don't see a good way to handle both the use cases above without a parameter for each of the above use cases (e.g., "store" and "AllowAsync").


For the "Asynchronous Access" use case, I think what the WCS has now seems fine except I would like to specify that the HTTP response code will be a 201 (Created). I assume the body is already defined as a XML coverage/manifest containing URLs to the data.

For the "Asynchronous Response" use case: If the client leaves out "AllowAsync" from their request, the server must either respond synchronously or with an exception that points to missing parameter "AllowAsync". If the client specifies "allowAsync=False", the server must either respond synchronously or with an exception pointing to a bad parameter value in "AllowAsync". If the client specifies "allowAsync=True", the server may respond synchronously or asynchronously. Where the asynchronous response would be an HTTP response code of 202 (Accepted). As the CR discusses, the body of the response should contain some indication of current status, some way to monitor the status, and an estimate of when it will be done. Should the CR include some suggestions for XML encoding of this information? I'm sure there are examples of this kind of thing in the SOAP/WS-* realm but I'm not familiar with that.


Ethan R. Davis                                Telephone: (303) 497-8155
Software Engineer                             Fax:       (303) 497-8690
UCAR Unidata Program Center                   E-mail:    edavis@xxxxxxxx
P.O. Box 3000
Boulder, CO  80307-3000             

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