<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Tom,<div><br></div><div>your suggested implementation has massive, inherent problems: it loses most of the benefits of a asynchronous interface!</div><div><br></div><div>By depending on a synchronous HTTP endpoint to run the query, your implementation breaks any time that synchronous thing times out, and it breaks if the network connection with the synchronous thing drops. In those cases, your UWS has no way to regain control of the query, even if the DB part is still running it. The UWS has to resubmit the query.</div><div><br></div><div>The whole point of UWS is <i>not </i> to depend on a synchronous HTTP-connection for long-running jobs.</div><div><br></div><div>You can build synchronous TAP as a wrapper around a UWS (Pat D. has done so) but it doesn't work the other way around.</div><div><br></div><div>Guy</div><div><br></div><div><br></div><div><div><div>On 6 Nov 2009, at 17:33, Tom McGlynn wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div>Hi Guy,<br><br>I'm not sure there is a big area of disagreement here. In terms of the text that users write and get back in the TAP asynchronous interface I'm not suggesting a that a single byte needs to be changed. It's all in what tasks are doing the processing. I've put in some text that I hope clarifies what I was saying below in context.<br><br><span class="Apple-tab-span" style="white-space:pre"> </span>Tom<br><br>Guy Rixon wrote:<br><blockquote type="cite">Tom,<br></blockquote><blockquote type="cite">whenever you use UWS in a service definition, you have to say what parameters it takes when setting up a job and the work done by that job. That's the "application of the UWS pattern" to use the terms from the UWS standard.<br></blockquote><br>I'm not sure I understand this. While there is talk of JDL and such in the UWS standard, I don't see any requirements that show it actually being used in any way. So while a given UWS implementation might restrict parameters being used, I don't see how that is done within the UWS protocol itself.<br><br><blockquote type="cite">The UWS specification is supposed to be reusable between applications; hence the U in the title. Therefore, it can't specify the application- specific parameters.<br></blockquote><blockquote type="cite"><br></blockquote><br>Right. I'm not suggesting that. What I'm saying is that it's easy to write a UWS that can handle any parameters -- as indeed you suggest you have done already below.<br><br><blockquote type="cite">It's possible to specify a UWS-conforming service for more than one application. CEA does this. The modern interface of this kind is called UWS-PA ("UWS for parameterized applications") and its fore- runner (which is SOAPy) is the Common Execution Connector. In these kind of services, the applications are pluggable.<br></blockquote>Sounds like the kind of thing I was looking at. I suggested in the original message that this has likely come up in earlier discussions.<br><br><blockquote type="cite">AstroGrid DSA/Catalogue has had a CEC interface for years. It uses a generic CEC implementation and passes the requests through to an ADQL- query application plugged inside it.<br></blockquote><blockquote type="cite">The downside of generalizing a job-control service in this way is complication and divergence from the synchronous case. TAP/UWS is quite like asynchronous TAP: you do an asynchronous query by POSTing the same parameters you could use for a synchronous query. If you try to use CEC or UWS-PA to start a TAP query then you have a different interface. Because that interface is more general, it's not as simple, either to implement in a service or to call from a client.<br></blockquote>Here's where I think I'm getting a little lost. My suggestion is the that I have a UWS service running above TAP that is simply a proxy for the TAP synchronous service. So by definition, they could not get disassociated. I'm getting the sense that for you, the UWS service needs to know about the parameters it's going to pass along to whatever it calls when it does a run. However, as far as I can see a UWS service can be entirely agnostic about parameters. It can simply take whatever parameters the user specifies and pass it along, leaving it to the underlying synchronous call to handle validity. In fact, for TAP that's pretty much the case since the names of the parameters used in TAP are not bounded.<br><br><br><blockquote type="cite">I think that the current boundary between TAP and UWS is just where we need it for the simplest implementations.<br></blockquote><br>I'm not so much concerned with boundaries as in the sense in which UWS is instantiated. Let me give a concrete example. I have a TAP service with a base URL of <a href="http://tap/">http://tap/</a>, so <a href="http://tap/sync">http://tap/sync</a> is the synchronous access point and <a href="http://tap/async">http://tap/async</a> is the async access point.<br><br>What happens when someone references the later URL? In my current implementation, a TAP servlet starts up, notes that I'm using an asynchronous request and calls the appropriate methods and classes that TAP has defined for this. If I had multiple asynchronous services these would likely be in a nice little UWS library. All is copacetic: UWS is a layer within TAP. It works fine but TAP and the UWS layer are pretty tightly coupled.<br><br>What I think I'm going to do when I get back from the IVOA is a bit different. When I invoke <a href="http://tap/async">http://tap/async</a> I start a servlet whose only knowledge of TAP is that there is a synchronous service at <a href="http://tap/sync">http://tap/sync</a>. It knows nothing of the internals of TAP and is completely independent of it. At some point the user does a <a href="http://tap/async/id/phase?phase=run">http://tap/async/id/phase?phase=run</a> and this UWS service takes the parameters that the user has specified for this job and invokes the <a href="http://tap/sync">http://tap/sync</a> URL with those parameters. The results get saved somehow and whenever the user sends the appropriate URL the results are sent back. The only thing the UWS service ever knows about TAP is the base URL. Everything else is supplied by the user.<br><br>Why do I like this better? Well it makes the TAP code simpler. It makes it easy for me to provide UWS functionality to all of my web services. E.g., I'd have a UWS interface to SkyView by simply changing the syncrhonous URL. And if UWS changes so that, e.g., there's now a security resource, I can plug it in without any change whatsoever to my TAP servlet. For me it will be a big win.<br><br>I'm not suggesting that this implementation be required. It would be fine to keep things coupled in one TAP implementation. However if the paradigm (and here I mean it in its literal sense of exemplar) is a UWS service runs on top of a TAP service then the way to describe the relationship between TAP and UWS changes. In particular I think it then makes a lot more sense to simply say that a UWS service can be used to provide asynchronous access to a TAP service. The standard can require that if we decide async access is mandatory (as I think we have). So the TAP document becomes simpler -- and far less tightly coupled with the UWS document.<br><br><blockquote type="cite">Cheers,<br></blockquote><blockquote type="cite">Guy<br></blockquote><blockquote type="cite">On 6 Nov 2009, at 15:33, Tom McGlynn wrote:<br></blockquote><blockquote type="cite"><blockquote type="cite">I'm sure everyone will be happy to see the word 'Final' in the title...<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">In the past couple of days I've gotten the UWS asynchronous implementation of TAP working (though doubtless still bug-ridden).<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">When I read and implemented the TAP and UWS standard I had the sense of UWS as being a layer within TAP. In retrospect I think it would have been better (for my implementation at least), if I had distinguished them more clearly.<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">Suppose we think of UWS not as an interface layer but as the definition of how to build an asynchronous proxies. UWS becomes a service definition, not an access protocol. The proxy accepts and caches input parameters from the users, starts the underlying request when told to, caches the response and sends it back to the user when requested. [I haven't followed the discussions of UWS earlier in the Grid list, so my apologies if I just discovering what everyone already knows....]<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">If I think of things this way, then I can implement UWS completely independently of the underlying application. Indeed the binding to the underlying application could be dynamic: I can provide a UWS layer over any number of distinct synchronous applications. I don't need to know anything about what parameters they use, just some root URL. The one piece of the specification that might cause problems is the desire to support multiple outputs as well as a single result. That's not at issue in TAP, but even this could easily be handled by returning a list of the outputs -- which is what UWS does now anyway.<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">UWS is not described this way in its standards document: it is shown as a layer within some bigger application, not as a separable entity. Similarly TAP shows the asynchronous interface tightly coupled within the rest of the TAP.<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">In this new view, the TAP document would say very little about the asynchronous interface. TAP itself would be synchronous, but if we want asynchronous access to be mandatory then the requirement is that a TAP implementation must specify a corresponding UWS service through which the TAP implementation can be invoked. We could still have a TAP service that is only available asynchronously: we allow that this TAP service is not directly callable: Only the associated UWS service can access it. I'm not trying to take sides here in the sync/async wars.<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">Changes to the UWS document would be rather more subtle, noting that the interface can implemented without reference to the underlying implementation, and perhaps explicitly supporting the kind of dynamic association with the underlying synchronous service mentioned above. Maybe provide a convenience resource to get the output in the single output case (rather than having to parse the output list).<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">The advantage had we taken this approach before, is that it largely decouples TAP and UWS. The TAP standard is shorter and simpler. The UWS standard is largely unchanged. We can change UWS in the future without worrying about any impact on TAP.<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">This is probably a bridge too far in terms of the TAP standard. For UWS it's really a change in tone more than content -- hints to the user -- so perhaps it is doable were it to be thought a good idea. Regardless, I do anticipate revising my own implementation to use this approach after the Interop.<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><span class="Apple-tab-span" style="white-space:pre"> </span>Tom McGlynn<br></blockquote></blockquote></div></blockquote></div><br></div></body></html>