[ogsa-wg] RE: GRIDtoday Edition: Tony Hey: 'Challenging Times for GGF & Standards'

[Dave Berry]

-----Original Message-----
From: owner-ogsa-wg at ggf.org [mailto:owner-ogsa-wg at ggf.org] On Behalf Of
Ian Foster
Sent: 03 March 2005 15:03

* Interactions with multiple resources: I think that's a red herring.
E.g., a job factory can return EPRs to WS-Resources representing jobs,
thus allowing individual jobs to be monitored and controlled, if needed.
The factory can also maintain a service group representing all jobs, and
then support operations that allow a client to "destroy all jobs that
match a certain pattern" (for example). It's not an either/or.


I'd like to drill down on this issue, because  to me it seems a rare
technical question amongst a sea of WS-FUD.  Tony has presented the case
in abstract.  DAIS raised a concrete example some months ago.  

The question, as I understand it, is how to send a single message to
multiple resources held by a given service using WSRF.  (The supposition
is that you know that these resources are accessible via the same
service).  I've had two possible patterns suggested to me that address
this question : 

1.  Pass multiple EPRs to an operation on the service 

2.  Use a service group 

To take these in turn, the first pattern is worth highlighting because
some  critics of WSRF assume that the only way to use an EPR is to call
an operation on it directly.  Of course this isn't true; you can
actually pass EPRs as arguments to another operation if that suits your
needs. 

The second pattern provides a single operation on a group of resources.
At first glance this seems to have the downside  that the server
controls which resources are in the set, rather than the client passing
in a list.   However, Ian's comment above suggests that the service
group can provide a mechanism that allows operations to be invoked on
subsets of the resources.  I don't know enough about service groups to
comment, except that this seems a reasonable solution.   

I would appreciate seeing these patterns explored in more depth  -
possibly in a face to face meeting next week?  From the above, it
certainly seems that the technical concern that Tony articulated can be
addressed. 

Dave.

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