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

> Mark,
> Either I am failing to articulate my point, or it is not compelling to

Jeffrey, quite possibly either of the above is true. Ditto for myself.

> There are pointers to things and there are contexts in which those things
> are used.

Alternatively, there are things that are used within a certain context and
that context implicitly (or explicitly) defines their behaviour and state.

> 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.

OK, I understand that, but how is that different to having a standard
(non-state specific) endpoint reference and associate the context (WS-RF
calls it context too) with the messages that are sent to that endpoint
reference? I don't see the technical difference, since both result in the
ability to contact and use the same stateful resource. Maybe there is
something that I'm missing that is specific to your use case? However, from
what Savas has said in the past and recently, maybe not. Any chance you
could address Savas' points?

>  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
> 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
> intended semantic of the references properties within a WS-Addressing EPR.

I think that might help only in terms of the English text: the point I'm
trying to make is that it doesn't matter if you call it a "fluffy white
kitten", as far as I can see, it's a context. The model you have defined
seems basically CORBA with XML/SOAP. It obviously works, since the OMG has
been doing that for years, but is it appropriate to an SOA, and particularly
if there is something already in that space that appears to provide the same

I thought I showed earlier (and William seemed to agree) that in the
examples that appear in WS-RF (the specs as well as the white paper)
WS-Context could have been used from the outset. There is no clear benefit
from embedding the "object id" (to take a CORBA term) into the IOR (oops,
should be WS-Address), when there's a context service. Actually, I'll
backtrack on that: there is only one benefit I can see and that is if you
only want to use a single resource/state. Like I said in another email, if
you want to group together resources into a multi-party/multi-state
interaction, then you or the application, will have to manage the individual
resources, remember their IDs, what combination of IDs makes sense in what
interaction, ... A definite headache if you're even contemplating using more
than 2 and possibly hundreds/thousands of states. Of course there are
solutions, like trading services, naming services, etc. but these have
drawbacks and start to make the "simple" approach much more complex.

The alternative, is to contextualise all of the interactions, so that each
service can opaquely bind a state to a specific context. Then all you have
to remember is the context within which you interacted with the services
(obviously you need to remember the services, but hey, you have to do that
in the WS-RF approach anyway).

> If I understand the intent of your transaction example, you would claim
> treatment of the input parameter of  a commit operation is another example
> of an appropriate use of WS-Context.

I argued that the use of the XID in conjunction with xa_switch_t (or
XAResource in J2EE) can be performed using 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,
> if transaction context flows with the message, they would say no.

After having written and worked on several transaction systems over the last
20 years, including for HP, I think I qualify as one of those "experienced"
individuals, and it's not as clear-cut as you might like others to believe:
the example illustrates how multiplexing across the same endpoint
(XAResource/xa_switch_t) with some contextual information (the XID) occurs
today in the real world; whether that contextual information is shipped as
an explicit transaction context in an IOR, for instance, or as an explicit
part of a message to the endpoint, is immaterial. As I said in the first
email to you: if you want to take a very restrictive view of context as
epitomised in a transaction service, then I can see a difference between
what you are looking at in WS-RF. However, WS-Context doesn't take such a
restrictive view point. Maybe if you read the specification again from a
more open perspective you'll begin to see that?

> 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.

Again, I think you're reading far too much between the lines here, combined
with a restrictive view of context (perhaps based only on transactions?) I
didn't mention registration of the commit operation with the transaction at
all, did I?

> If I follow your line of reasoning, then why don't we treat all web
> request parameter data as WS-Context elements? If you use the term
> "context" this broadly and indiscriminately, one might argue that all
> 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.

It is certainly possible that for some interaction patterns much more
information, such as properties, *could* be embedded within a WS-Context.
And this precisely matches at least one of the use cases that we have been
asked to support. Check out the TC pages and the public mailing lists and
you'll find the examples.

If you have such strong views on what WS-Context should and should not do,
then maybe you should participate in the WS-Context technical committee?

The current intent of WS-Context is to provide a flexible and extensible
associative scheme for messages, that can accomodate a number of different
use cases. It is certainly not an "indiscriminate" use of the term context.

You may also want to check out the OMG's Additional Structuring Mechanisms
for the OTS and JSR 95 (a J2EE version of the previous spec) both of which
IBM worked on with myself and several others from the WS-CAF team. In both
specs there is the notion of a general extended context that contains
properties/data/etc that is shipped on invocation requests and is required
at the endpoint in order to perform the operation. From what I've been told,
I believe that IBM and its customers use this pattern quite a bit.

Let me reiterate: WS-Context is intended to support a number of different
use cases. Although the notion of shipping state and properties in the
context of a message in order that the recipient can then use that
information to perform the desired operation is not necessarily a common
requirement, it is one that we currently believe that WS-Context should

> And it would not be
> consistent with the well known and traditional meaning of message
> context as it has been used in distributed systems for years.

If you believe that context needs to be so restricted, then please get
involved in the TC.

However, we still seem to be going round in circles. Maybe I can try to
summarise where I think we are, and if I'm wrong, please feel free to
correct me:

you believe that WS-Context should have a very narrow (transaction-type)
view of what a context is. In that situation, you would say that it is an
inappropriate use of context for the endpoint to tie it to state.
Furthermore, the model you prefer for identifying states (or object
instances) within a service is essentially similar to CORBA, but with XML
and SOAP.

whereas, the WS-Context view is that context isn't narrowly defined and that
this is a SOA we're dealing with, where services shouldn't necessarly expose
their backend implementation choices to the world.


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


> 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
> 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
> work
> that may be implied by the receipt of those messages.
> I think we're agreed that context goes beyond transactions, but if you
> 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
> to
> 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
> 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
> 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
> together
> 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:
> <wsa:EndpointRefrence>
>     <wsa:Address>
>         http://....
>     </wsa:Address>
>     <wsa:ReferenceProperties>
>         <tns:resourceID>C</tns:resourceID>
>     </wsa:ReferenceProperties>
> </wsa:EndpointReference>
> the same thing can be achieved using context (in pseudo-code):
> <wsctx:context>C</wsctx:context>   <--- appears in the header block
> <wsa:Address>
>     http://
> </wsa:Address>
> 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
> 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
> whereas in WS-Context it's in the header. But something (whether you call
> it
> an interceptor, XML processor handle, or whatever) has to pick apart the
> message.
> 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
> redefine
> them?
> 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
> via context also appears to be a lot easier when you have mutliple
> 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
> and
> 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
> need
> to tie together into a collaborative effort. What I mean by this is that
> the
> invoker of those multiple stateful services would need to remember each of
> the resourceIDs (or rather their unique EndpointReference). That seems
> a rather heavyweight approach and one which appears to have scaling
> problems.
> 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
> context
> does not have to be produced by the client in WS-Context and in fact can
> 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
> context can also support that. WS-Context has an explicit (though
> context element for identifying the endpoints that are participating in an
> interaction.
> So, in conclusion, I may be totally off-base here in my understanding of
> the
> 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
> 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.
> ----
> 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
> introduced with the WS-Resource. There is no need to declare the
> WS-Resource context for interoperability reasons. The WS-Resource
> 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
> 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
> |
>   |
>            |
> ---------------------------------------------------------|
> Eric:
> We (the WSRF authors) are very familiar with WS-Context and certainly
> 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
> seeing to the proposal from the IBM and HP Web services teams, as well as
> many others.
> Ian.
> 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
>       (http://www.neresc.ac.uk/ws-gaf).
>       Regards,
>       --
>       Savas Parastatidis
>       http://savas.parastatidis.name
>       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
>       CORBA.
>       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
>       origin.
>       I also agree that I can't see a practical difference between context
>       management in transactions and the context management defined for
>       Resource Framework.
>       It would be nice to try to converge these things at some point and
>       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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