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Subject: RE: [ogsi-wg] RE: [ws-caf] WS-Resource Framework

Actually I think this helps a lot.  If I understand correctly, the WS-RF was trying to construct a pointer to an instance of a resource managing persistent state.  Whereas WS-Context is trying to create a mechanism for managing persistent state external to resources, and in some cases used by the resources in performing coordinated operations.  

On the commit topic -- A commit on a single resource is very different than a commit across multiple resources, and by definition requires persistent context outside the scope of a single resource manager.

In any case what it seems like to me now is that WS-RF is an attempt to define a substitute for the URL based addressing typically used in Web services, for the specific purpose of addressing a resource.  If so, this would seem to provide a useful bit of context since database and file sessions are usually scoped to an operating system process or mainframe region.  Although they are sometimes network-addressable there is no standard format for them.

In this way WS-RF could also be used as a pointer to a WS-Context instance, in the situation in which the persistent state may have to be managed externally to a more permanent resource like those WS-RF points to.

-----Original Message-----
From: Jeffrey Frey [mailto:jafrey@us.ibm.com]
Sent: Tuesday, January 27, 2004 1:01 AM
To: Mark Little
Cc: Newcomer, Eric; Ian Foster; ogsi-wg@gridforum.org;
owner-ogsi-wg@gridforum.org; Savas Parastatidis;
Subject: Re: [ogsi-wg] RE: [ws-caf] WS-Resource Framework

Either I am failing to articulate my point, or it is not compelling to you.
There are pointers to things and there are contexts in which those things
are used. What we intended to represent with the endpoint reference in WSRF
is a structured pointer to a stateful resource. We purposely encapsulate
the identity of the resource in the endpoint reference so that the EPR
could be passed and used as a network-wide resource pointer.  This
eliminates the need to treat the pointer to a stateful resource as two or
more separate components in the programming model, namely the network
endpoint address of the agent providing access to the resource, and a
context element needed to further qualify the resource instance at that
endpoint.  This is the primary rationale for treating the resource identity
as part of the service endpoint reference. If it would help eliminate the
confusion, I would be happy to stop using the word "context" to express the
intended semantic of the references properties within a WS-Addressing EPR.

If I understand the intent of your transaction example, you would claim the
treatment of the input parameter of  a commit operation is another example
of an appropriate use of WS-Context. I argue that the use of the XID to
identify the stateful resource (transaction state) as the explicit target
of the commit operation is not same as the treatment of the XID as a
"transaction context" that accompanies a request message to a database
targeting a stateful resource (database content) in the database. In both
examples, the same XID value is used, and it represents the same
transaction. But in one case it is used to express a contextual use of the
database content (an appropriate use of WS-Context) and in the other it
represents the primary target of the request message (Commit) itself.   If
you ask a person experienced in building transaction systems whether a
commit or rollback message is performed in the context of a transaction, or
if transaction context flows with the message, they would say no. There is
no need to register the execution of the commit operation in the
transactional unit of work, even though there is a need to identify the
transaction being committed. These are distinct ideas.

If I follow your line of reasoning, then why don't we treat all web service
request parameter data as WS-Context elements? If you use the term
"context" this broadly and indiscriminately, one might argue that all input
required for the execution of a service request is "context" for the
request. In fact, one could then argue that "context" not only represents
the content of the request message, but all of the environmental state
needed, however obtained or provided, in the support of the execution of
the request. Of course, all of this is "context". But it is not a useful
way to express or use the notion of WS-Context. And it would not be
consistent with the well known and traditional meaning of message execution
context as it has been used in distributed systems for years.

Jeffrey Frey

IBM Distinguished Engineer
OnDemand System Architecture and Design
Phone: 845-435-3067  Tie: 8-295-3067  Cell: 914-456-6556
Notes: Jeffrey Frey/Poughkeepsie/IBM@IBMUS
Internet: jafrey@us.ibm.com

|         |           "Mark Little"    |
|         |           <mark.little@arju|
|         |           na.com>          |
|         |                            |
|         |           01/24/2004 06:05 |
|         |           AM               |
|         |                            |
  |                                                                                                                                    |
  |       To:       Jeffrey Frey/Poughkeepsie/IBM@IBMUS, "Ian Foster" <foster@mcs.anl.gov>                                             |
  |       cc:       "Newcomer, Eric" <Eric.Newcomer@iona.com>, <ogsi-wg@gridforum.org>, <owner-ogsi-wg@gridforum.org>, "Savas          |
  |        Parastatidis" <Savas.Parastatidis@newcastle.ac.uk>, <ws-caf@lists.oasis-open.org>                                           |
  |       Subject:  Re: [ogsi-wg] RE: [ws-caf] WS-Resource Framework                                                                   |
  |                                                                                                                                    |

Jeffrey, after having read through the WS-R specifications, I fail to see
any subtle or not-so-subtle distinction. Maybe this is due to
misundertanding of WS-R on my part, or perhaps a misundertanding of
WS-Context on yours, but I'd like to explore the perceived mismatch.

Whilst it is true that the types of context to which you refer allow for an
interoperable understanding between client and server, I think that misses
the real point of WS-Context in general: to allow the unambiguous
correlation of a set of messages sent to a (set of) endpoints in an
implementation (or context specific) manner; the endpoint may use that
context to associate a specific state to itself prior to performing any
that may be implied by the receipt of those messages.

I think we're agreed that context goes beyond transactions, but if you take
transactions for a second, let's look at the X/Open XA specification and
particularly how a type of context is used within that. Within XA,
transactions are identified by XIDs and a given resource manager
(essentially the entity that controls the way in which data is transacted
a back-end database) may multiplex across many different transaction
instances. So, for example, in the C API for XA, there is a struct
(xa_switch_t), that has operations for preparing, committing, rolling back
etc. transactions and each of those operations takes an XID to identify the
transaction (state) on which it should operate: only one instance of the
struct exists. So, you could have an XA service that receives messages to
commit (say) a transaction and the context for that message would be an XID
that the service uses to determine which state instance to manipulate.

What I hope I've illustrated is that context isn't just used to tie
endpoints for interoperability: it can be used to unambiguously identify
stateful instances in precisely the same way that is shown in the example
pattern from the ModelingState (page 12). Or did I miss something?

In fact, if we look at the schema from that example:


the same thing can be achieved using context (in pseudo-code):

<wsctx:context>C</wsctx:context>   <--- appears in the header block


The endpoint that receives both message types has to parse the message and
determine the circumstances in which it can be used, i.e., in this case the
state to which it should be applied. The only difference I can see is that
in WS-R, the context for the message is embedded in the endpoint reference,
whereas in WS-Context it's in the header. But something (whether you call
an interceptor, XML processor handle, or whatever) has to pick apart the

You say that there's nothing extra needed in terms of a handler over and
above what's already in WS-Addressing, but isn't that just saying that
because you leverage something that has handlers, you don't have to

And in both cases it can be just as opaque to client and service.

Although your interpretation of how WS-Context *may* be used is certainly
correct, the fact is that we've seen many different use cases for context
that show the general notion of a context should not be limited to a
specific use case. Identifying state at an endpoint is possible by a
correlation id (e.g., a cookie), and in fact state can be encoded within a
context for purely stateless services.

I think as Savas started to elucidate, identification of stateful instances
via context also appears to be a lot easier when you have mutliple services
in the same interaction. With context, the invoker of a set of services
would typically selects the relevant context id that represents a specific
set of stateful services and all of the services see the same context id
map that to whatever state is appropriate for that interaction. It would
appear from the WS-R documents that in a similar scenario, each stateful
service generates a different resourceID that somehow the invoker would
to tie together into a collaborative effort. What I mean by this is that
invoker of those multiple stateful services would need to remember each of
the resourceIDs (or rather their unique EndpointReference). That seems like
a rather heavyweight approach and one which appears to have scaling

You also mention that the WS-R "context" is only produced by the service,
rather than by the client in WS-Context. However, that's wrong - the
does not have to be produced by the client in WS-Context and in fact can be
augmented by each service. So, a "blank" context could be received by a
service that then operates on some state which the client needs to
unambiguously identify later, and in which case the service can add the
state identification to the context that flows back to the client (or
recipient of the response).

It may be that the model outlined in the WS-R documents for representing
stateful instances is more ideal for the Grid environments in which it has
evolved. But in that case, it's worth pointing out that a generic notion of
context can also support that. WS-Context has an explicit (though optional)
context element for identifying the endpoints that are participating in an

So, in conclusion, I may be totally off-base here in my understanding of
WS-R specifications, but I don't see a distinction between them and what
WS-Context is attempting to achieve. If you take a very restrictive view of
what context is, then I can understand why you may think there are
differences. However, we haven't taken that restrictive view. Maybe its
approaching the same problem from different ends of the spectrum and in
which case I'd echo Eric's original question about whether some level of
convergence makes sense.

All the best,


Mark Little,
Chief Architect, Transactions,
Arjuna Technologies Ltd.

----- Original Message -----
From: "Jeffrey Frey" <jafrey@us.ibm.com>
To: "Ian Foster" <foster@mcs.anl.gov>
Cc: "Newcomer, Eric" <Eric.Newcomer@iona.com>; <ogsi-wg@gridforum.org>;
<owner-ogsi-wg@gridforum.org>; "Savas Parastatidis"
<Savas.Parastatidis@newcastle.ac.uk>; <ws-caf@lists.oasis-open.org>
Sent: Friday, January 23, 2004 6:11 PM
Subject: Re: [ogsi-wg] RE: [ws-caf] WS-Resource Framework

I agree with Ian. There is a subtle but important distinction. Context, as
referred to in WS-Context, is explicitly declared and meant to facilitate
an interoperable understanding between the client and the service. For
example, a transactional unit of work is something that can be established
by the client and sent to the service in a well known context that
accompanies the message to the web service. The same is true for contexts
that represent security function, etc. This is not the same as what we have
introduced with the WS-Resource. There is no need to declare the
WS-Resource context for interoperability reasons. The WS-Resource "context"
is not produced by the client. It is produced and consumed by the service.
It is carried in the EPR as an opaque construct to the client. There is no
need for the client to interpret or inspect the contents of the reference
properties. In fact, there is no additional "context" handler required at
all on the client side of the interaction other than what is already
generically specified in the WS-Addressing specification. So, while I can
understand that this appears to be the same at an abstract level of
understanding, we did not intend the identity of the resource as it is
treated in the EPR to be interpreted as "context" in the same way other
usage context is produced and consumed across the web service interaction
with the client.

In addition, while we know some have an aversion to the treatment of the
stateful resource as a "first class" addressable entity or as the implied
target of the interaction from the client., some do not. And if your view
is that the resource is the "target" of the message interchange from the
client the service, our view is that it should be treated as distinct from
other execution contexts which exist not for the purpose of identifying the
target of the message exchange, but to provide additional control over how
the target of the message exchange is to be treated. WS-Context should be
used to facilitate the contextual usage of the target of the message, not
the target of the message itself.

Jeffrey Frey

IBM Distinguished Engineer
OnDemand System Architecture and Design
Phone: 845-435-3067  Tie: 8-295-3067  Cell: 914-456-6556
Notes: Jeffrey Frey/Poughkeepsie/IBM@IBMUS
Internet: jafrey@us.ibm.com

|         |           Ian Foster       |
|         |           <foster@mcs.anl.g|
|         |           ov>              |
|         |           Sent by:         |
|         |           owner-ogsi-wg@gri|
|         |           dforum.org       |
|         |                            |
|         |                            |
|         |           01/22/2004 05:34 |
|         |           PM               |
|         |                            |


  |       To:       "Savas Parastatidis"
<Savas.Parastatidis@newcastle.ac.uk>, "Newcomer, Eric"
<Eric.Newcomer@iona.com>               |
  |       cc:       <ws-caf@lists.oasis-open.org>, <ogsi-wg@gridforum.org>
  |       Subject:  Re: [ogsi-wg] RE: [ws-caf] WS-Resource Framework




We (the WSRF authors) are very familiar with WS-Context and certainly agree
that it has an important role to play.

However, we also believe that there are important situations in which
stateful resources need to be identified and managed as first-class
entities: thus WS-Resource Framework. Thus the enthusiastic response we are
seeing to the proposal from the IBM and HP Web services teams, as well as
many others.


At 10:06 PM 1/22/2004 +0000, Savas Parastatidis wrote:

      Dear Eric,

      I agree with your comments. In fact, back in August 2003 we used
      WS-Context as an example of how stateful interactions and/or
      distributed units of work could be modelled. This was part of our
      proposals for a WSA-friendly framework for building Grid applications


      Savas Parastatidis

      From: Newcomer, Eric [mailto:Eric.Newcomer@iona.com]
      Sent: Thursday, January 22, 2004 6:28 PM
      To: Mark Little; Savas Parastatidis; ws-caf@lists.oasis-open.org
      Subject: RE: [ws-caf] WS-Resource Framework

      I have the general impression of the OGSA specs as the equivalence of

      On the topic of the WS-Resource Framework in particular, I've looked
      through the specs and I think WS-Context could have been used, and
      it's unfortunate it wasn't.  I suppose the Resource Framework effort
      grew out of the Grid work however so it has a completely independent

      I also agree that I can't see a practical difference between context
      management in transactions and the context management defined for the
      Resource Framework.

      It would be nice to try to converge these things at some point and in
      some organization - is that OASIS?

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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