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

[Ian Foster]

Tony:

I think your message captures nicely (although perhaps inadvertently!) the 
way in which people are talking past each other in this discussion.

I would never say that the "messages to single resources approach" is the 
"the foundation for all operations on all services." I understand that some 
people in this strange religious debate that we've fallen into have 
characterized things that way, but that's far from the truth.

 From my perspective, WSRF was motivated by our experiences building 
"service oriented infrastructure", and seeing that the same patterns were 
occuring repeatedly in different places as we built systems to manage Grid 
systems. The codification of those patterns in standard (and 
WS-I+-compliant, I like to emphasize) WSDL has allowed us to simplify many 
aspects of both service implementation and client tools. Others report the 
same positive experiences. The introduction of WS-Transfer, which provides 
similar functionality and seems to be intended for similar purposes, 
suggests that there is broad recognition of the importance of these 
patterns. However, the fact that these patterns are useful in building 
certain classes of management applications (a primary focus of OGSA, by the 
way) certainly doesn't mean that they are appropriate everywhere.

I'd also like to suggest that when considering the assertion that "sending 
messages to single resources makes systems fragile", it is useful to 
recognize that the messages sent over the wire when using an EPR to a 
WS-Resource (the WSRF approach) vs. an EPR plus a context id (e.g., as in 
the eCommerce systems that are often mentioned) are close to identical. In 
fact, the only difference is really just the location of the "context id": 
in the EPR vs. in the body of the message! I don't see how the choice of 
one placement vs. the other can render a service "robust and scalable" vs. 
"fragile and nonscalable"--especially as the service itself can be 
implemented in an essentially identical manner in the two cases.

My preceding paragraph suggest that there are opportunities for common 
ground, and I suspect that is the case. However, to find that common ground 
we need to identify clearly just what it is we are trying to do and then 
address different issues separately. I believe that there are far too many 
different issues being mixed together at present for useful progress to 
occur. Unfortunately, I'm not sure how to proceed to separate out the 
different issues.

Ian.

At 11:37 AM 3/3/2005 +0000, Tony Hey wrote:
>The point is not about how well the WS-RF and WS-Transfer stacks compare
>but rather whether it is always appropriate to use the "messages are
>directed at single resources" approach? Many people, including people
>whose technical judgement I respect such as Tony Storey, Ian Foster,
>Dave Snelling and others, apparently believe that the answer to this
>question is "everywhere: it is the foundation for all operations on all
>services". It is therefore not surprising that this group do not see the
>need to worry about the question "is it a good idea to build
>architecture around the idea of sending messages to single resources?"

_______________________________________________________________
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
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