RE: [ogsa-wg] RE: Modeling State: Technical Questions
Savas: I think your email misses the point of the current discussion. Of course, as you point out, if I have a handle of some sort for a job (a WS-Addressing EPR, as in WSRF/WS-Transfer, or a job-id, as you advocate below), then I can include several of these in a request to the job factory asking for some operation to be performed on them all. I don't believe that anyone's debating that. But that's not the topic of the recent thread. What Mark and Karl are discussing is how you would express more abstract requests such as "kill all jobs that have consumed more than one hour's CPU time." This is a question of query languages, I presume, not modeling of job ids. Ian. At 01:10 PM 4/5/2005 +0100, Savas Parastatidis wrote:
Dear all,
I think something needs to be clarified with regards to handling multiple jobs with one message. The beauty of document-oriented interactions is that you can do things like...
<job-details-request> <job-id>urn:ogsa:job:guid:bla-bla-bla-001</job-id> <job-id>urn:ogsa:job:guid:bla-bla-bla-010</job-id> <job-id>urn:ogsa:job:guid:bla-bla-bla-002</job-id> <job-id>urn:ogsa:job:guid:bla-bla-bla-029</job-id> </job-details-request>
Or
<job-suspend-request> <job-id>urn:ogsa:job:guid:bla-bla-bla-002</job-id> <job-id>urn:ogsa:job:guid:bla-bla-bla-005</job-id> <job-id>urn:ogsa:job:guid:bla-bla-bla-008</job-id> </job-suspend-request>
The schema for the above document can allow anything from 0 to N number of <job-id> elements.
What WS-RF and WS-Transfer and REST are doing is require that each message be directed to only one resource. As a result, when it comes to defining groups of resources, additional resources (representing collections) have to be created. Populating and managing the collections require additional messages.
The WS-RF/Ws-Transfer/REST model is a special case of the document-oriented model I described above...
<!-- just one resource all the time --> <job-suspend-request> <job-id>urn:ogsa:job:guid:bla-bla-bla-002</job-id> </job-suspend-request>
In the WS-RF/WS-Transfer case the job ID will have to be part of the wsa:To (wsa -> WS-Addressing) header. In REST, it is the URI on which the operations are called (if we are using HTTP and the HTTP verbs, then the URI usually has the 'http' prefix).
An example, of a WS-Addresing EPR...
<my:MyEndpointReference> <wsa:Address> urn:ogsa:job:guid:bla-bla-bla-002</wsa:Address> </my:MyEndpointReference>
Please note that the address doesn't have to carry transport/transfer specific semantics (i.e. it doesn't have to be an 'http' URI). The above would require a registry look up if that's necessary or perhaps a P2P network that will know how to direct the message to its destination based only on the above information. The sender of the message may never actually see the transport-specific address of the receiving service.
This means that a SOAP msg like the one bellow will have to be sent...
<soap:Envelope> <soap:Header> <wsa:To>urn:ogsa:job:guid:bla-bla-bla-002</wsa:To> </soap:Header> <soap:Body> <job:job-suspend-request /> </soap:Body> </soap:Envelope>
Well... it turns out that this can by the special case of a message that looks like this...
<soap:Envelope> <soap:Header> <wsa:To>urn:ogsa:job:service:Newcastle-Job-Service</wsa:To> <!-- again... a registry lookup although http://ncl.ac.uk/job-service could have also been used --> </soap:Header> <soap:Body> <job:job-suspend-request> <job:job-id>urn:ogsa:job:guid:bla-bla-bla-002</job:job-id> <job:job-id>urn:ogsa:job:guid:bla-bla-bla-003</job:job-id> <job:job-id>urn:ogsa:job:guid:bla-bla-bla-004</job:job-id> </job:job-suspend-request> </soap:Body> </soap:Envelope>
What WS-RF and WS-Transfer seem to be doing is to expose to the wire the programming abstraction that most of us are used to (i.e. calling methods on an object). As a result, systems based on a special case are designed rather than the more general case. It's been our argument all along that this may not be the most efficient way of designing systems in general (perhaps in certain application domains the WS-RF/WS-Transfer approach may be appropriate) but I am prepared to be corrected on this :-)
Best regards, -- Savas Parastatidis http://savas.parastatidis.name
_______________________________________________________________ Ian Foster www.mcs.anl.gov/~foster Math & Computer Science Div. Dept of Computer Science Argonne National Laboratory The University of Chicago Argonne, IL 60439, U.S.A. Chicago, IL 60637, U.S.A. Tel: 630 252 4619 Fax: 630 252 1997 Globus Alliance, www.globus.org
Hi all,
But that's not the topic of the recent thread.
So I'm changing the subject... :-)
What WS-RF and WS-Transfer and REST are doing is require that each message be directed to only one resource. As a result, when it comes to defining groups of resources, additional resources (representing collections) have to be created. Populating and managing the collections require additional messages.
I think your email misses the point of the current discussion.
Of course, as you point out, if I have a handle of some sort for a job (a WS-Addressing EPR, as in WSRF/WS-Transfer, or a job-id, as you advocate below), then I can include several of these in a request to the job factory asking for some operation to be performed on them all. I don't believe that anyone's debating that.
I think that a *part* of this discussion can be summarized as "what is the level of abstraction of the interfaces you use"? Which between a low-level resource-oriented (probably per-resource) interface and a high-level abstract interface is the best one? My answer so far is "both". You want to deal both with resources ("deploy this OS on this specific host"), and to have a high-level interface ("start me these zillion jobs, wherever and whenever suitable"). Operations in the high-level interface will generate operations in the low-level interfaces (when you start a job with the high-level one, you might deploy the OS beforehand). The high-level interface might show some of the operations of the low-level interface ("what is the state of this specific job?"). Which takes me to the execution management in OGSA. We are now doing the container, which for me seems to be a resource with low-level interfaces (not as low as the bare metal though). But I think the container's interfaces, while needed, are not the high-level interfaces yet, and these too are needed. Do you have any wisdom (*) on this issue, for OGSA as a whole? BTW, the issue above applies to other OGSA capabilities also. By the way, I'm not including angle brackets, SOAP and WSA issues on the above. What will be put in resource properties is affected, but I'm not going down to these details yet. Regards, Fred Maciel. (*) No conscious reference to WSDM intended, only subconscious and subliminal ones :-).
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Fred Maciel -
Ian Foster