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

[Hiro Kishimoto]

Andy's email bounced.
----
Hiro Kishimoto

Subject: RE: [ogsa-wg] RE: GRIDtoday Edition: Tony Hey: 'Challenging   Times for
GGF & Standards'
Date: Thu, 3 Mar 2005 16:25:09 -0000
From: "Andrew Herbert" <aherbert at microsoft.com>

Ian, Tony

This discussion reminds me very much of the early history of CORBA, when there
was a create debate between those who believed dynamic interface types were
central to object request broking and those who thought they were the spawn of
the devil.  Both approaches were able to emulate the other and so any argument
about which was the more fundamental was sterile.  There was certainly an
element of bias towards different styles of application, and this was what split
the OMG community since each camp had an legacy to carry forward and an
investment in their view of the future.  The OMG architecture was therefore
positioned at a level where both approaches could be accommodated and as CORBA
and CORBA Services were defined a case by case view was taken of the need for a
static or dynamic interface, or both, or some unification of the two. It led to
optional elements and even some duplication of function in the early OMG
specifications, but as the standards process unfolded and users gained
experience with the technology it became easier to make rational choices and if
necessary go back and fix the specifications. Of course vendors initially
implemented just the options they preferred but over time they converged on
common components and interfaces.  And of course the users also demanded
interoperability between CORBA and DCOM and got it, even though for many CORBA
vendors DCOM was "the enemy".

 

The academic question of the superiority of one style of object request broking
over another was never actually resolved - a workable hybrid evolved which meet
the needs of the users and the OMG moved on. Interestingly given your comment
about the position of names in messages, with hindsight many of the CORBA
debates were ultimately a fight about where names stood relative to "dot",
"comma", "bra" and "ket" in object invocation semantics and fifteen years later
I find it hard to remember the passions that made these things seem so important
at the time.

 

Ian positions the "primary purpose" of OGSA as being "certain classes of
management application".  The problem Tony and others appear to be grappling
with is the desire to have OGSA as the architecture for broader notions of "Grid
Computing" and "e-Science" and this is where the shoe starts to pinch.  Ian asks
how to make progress.  It seems to me that GGF has two choices - make the scope
of OGSA narrow so those interested in "certain classes of management
application" can develop an architecture for this unimpeded, or make the scope
of OGSA broader and admit to the possibility of other classes of application of
interest to the GGF community.

 

I observe colleagues I respect building systems that clearly are doing "Grid
Computing" of the kind envisioned in Ian and Karl's book that coined the
concept, and these people seem to manage to build and operate their systems
without invoking WSRF so this makes me wary of any architecture for "Grid
computing" and/or "e-Science" which mandates WSRF in its entirety in all cases. 

 

Andrew

________________________________

From: Ian Foster [mailto:foster at mcs.anl.gov] 
Sent: 03 March 2005 07:04
To: Tony Hey; Frank Siebenlist
Cc: Dennis Gannon; Samuel Meder; ogsa-wg; paul.watson at ncl.ac.uk;
dave.pearson at oracle.com; savas.parastatidis at ncl.ac.uk; Jim Gray;
humphrey at cs.virginia.edu; grimshaw at virginia.edu; Andrew Herbert;
gcf at indiana.edu; mark.linesch at hp.com
Subject: RE: [ogsa-wg] RE: GRIDtoday Edition: Tony Hey: 'Challenging Times for
GGF & Standards'

 

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 <http://www.globus.org/>