UWS Parameters: What is "isPost"?

[Paul Harrison]

> On 17 Jun 2024, at 02:23, Joshua Fraustro via grid <grid at ivoa.net> wrote:
> 
> I opened a ticket on the UWS github repository here: https://github.com/ivoa-std/UWS/issues/4 [github.com], but I figured there was a broader reach of some folks who might know the answer.
> 
> The UWS specification for "uws:Parameters" lists a boolean XML attribute of "isPost". None of the current versions of the UWS specification (XSD or document) have any description or documentation on the attribute and, as far back as I can search, haven't since its quiet addition in an early draft of UWS 1.0.
> 
> Is anyone familiar with the original intention of the attribute? Is anyone actually using it?


It is an artefact of the fact that the UWS evolved from a similar service called CEA that Astrogrid developed. The name is probably not that great, but the original description looked like

 "is the original job creation post simply an opaque post that cannot be easily fitted into the parameter model,
          then a single 'parameter' description should be returned with this set to true”


The motivation for it was that some of the early web services were just a wrapper around some commandline application that was driven by a config file. It was then relatively easy just to POST that file to the job creation end-point to create the job. This use case is not quite covered by the idea of “by reference” parameters, as clearly you need to find somewhere to put the original file that is http addressable, which requires more work on the client side.

Clearly it was an oversight that it crept into the final standard schema, but I think that probably came about from the schema being copied from a real running UWS implementation at the time (and that it was put in to work with a real existing CEA client), and I forgot to remove it.

Taking a step back the original “vision” of UWS was that it was mostly about the control and description of the “job model” and that the “Job description language” that described the “input” to the job was a separate concern. This got blurred from the original CEA view of the world to include more “parameter” description in the base UWS as the stanardization process continued. I have been trying to advocate separating the parameter description concerns again in several places. - e.g. in DataLink

Regards,
	Paul.
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