RE: i009 - mustIgnore rule for multiple To, ReplyTo, etc.

One of the scenarios that I imagine is a future version of
WS-Addressing.  IF WS-Addressing V1.0 builds in a "substitution
mechanism", then I think it can enable a WS-Addressing V.Next to be
forwards and backwards compatible with V1.0.

Imagine WS-A V.Next decides that for
reliability/scalability/performance/protocol/whatever reasons, that
there can be multiple ReplyTos or FaultTos in a message.  The meaning of
multiple *Tos is that the client can select which to use at its
discretion.  

Because these *Tos are both backwards and forwards compatible, WS-A
V.Next decides to re-use the WS-A namespace name for this compatible
change to the semantics of multiple *Tos.  

We have the best of both worlds now: WS-A V.Next receivers can receive
*Tos from WS-A V1.0 and V.Next senders, and WS-A V1.0 receivers can
receive *Tos from WS-A V1.0 and V.Next senders.

If there is no "ignore" mechanism in place, the situation is harder,
though not impossible.  WS-A V.Next would need to introduce new QNames,
perhaps wsav2:ReplyTo and wsav2:FaultTo.  These Qnames have the same
functionality described earlier, multiples are allowed and client can
choose.  These Qnames must say that they replace the wsav1 Qnames in the
case of where messages contain both v1 and v2 *Tos.  To enable
compatibility, 2 things must be specified.  Forwards compatibility
requires that the sender must send both wsav2:*To AND wsav1:*To in
messages.  The wsav2:*To would obviously be marked with mU="false".
Backwards compatibility requires that the sender must understand both
wsav1:*To and wsav2:*To elements.

I think that design #1, which is roughly Must Ignore Extras, allows for
a simpler and more natural backwards and forwards compatibility.

Cheers,
Dave

> -----Original Message-----
> From: public-ws-addressing-request@w3.org
[mailto:public-ws-addressing-
> request@w3.org] On Behalf Of paul.downey@bt.com
> Sent: Wednesday, January 12, 2005 1:48 PM
> To: tim@mindreef.com
> Cc: public-ws-addressing@w3.org
> Subject: RE: i009 - mustIgnore rule for multiple To, ReplyTo, etc.
> 
> Hi Tim!
> 
> from my POV helpful expert comments like yours and Noah's are always
> welcome
> and has to be one of the main reasons why a WG uses a public list for
> technical
> discussions.
> 
> You've raised some interesting points here and. Doug Davis also raised
the
> targeted
> role issue offline, so you're not alone with your concerns.
> 
> In many respects the difficulties you raise around allowing multiple
> instances of a
> should come as no surprise to me given the explosion of complexity was
the
> main reason my raising this issue in the first place. i guess it
possibly
> serves me
> right for looking for an easy way out! i'll noodle on this a little
more
> before our
> discussion on this issue next week.
> 
> thanks,
> Paul
> 
> 	-----Original Message-----
> 	From: public-ws-addressing-request@w3.org on behalf of Tim Ewald
> 	Sent: Wed 12/01/2005 19:55
> 	To: Downey,PS,Paul,XAGA C
> 	Cc: public-ws-addressing@w3.org
> 	Subject: RE: i009 - mustIgnore rule for multiple To, ReplyTo,
etc.
> 
> 
> 
> 
> 	Paul,
> 
> 	Like Noah, I'm not a member of the WSA group, so feel free to
tell
> me to go
> 	away (unlike Noah I didn't add this disclaimer to earlier posts;
> sorry).
> 
> 	Speaking as someone who works at a company dedicated to helping
> people deal
> 	with interoperability problems, I have to question the wisdom of
> allowing
> 	but ignoring multiple instances of these headers. Presumably a
SOAP
> node
> 	would only inject an additional duplicate header to achieve a
> desired
> 	effect. To ensure that effect, the processor would have to check
to
> see
> 	whether the same header already existed in a message. If it did,
the
> 	processor would presumably either raise an exception or put it's
> header in
> 	*before* the present header in order to trump it. There would be
> little
> 	reason to put it in after the existing header, since it would
just
> be
> 	ignored.
> 
> 	This raises two questions in my mind. First, what are the
security
> 	implications? Will this open to WSA to attacks based on shifting
> relative
> 	position of a header and require the use of XPath expressions in
> signatures
> 	that explicitly specify position relative to soap:Header? If
> multiple
> 	instances were disallowed, this issue would go away as injecting
a
> duplicate
> 	header would invalidate the message.
> 
> 	Second, how does all this work relative to headers targeted at
> different
> 	actors/roles (are those allowed with WSA?)?
> 
> 	While I can see applying the mustIgnore rule to content you
don't
> know
> 	about, it seems kind of strange to apply it to duplicate
elements in
> a given
> 	spec. If SOAP allowed multiple soap:Header/soap:Body elements in
any
> order,
> 	with only the first of each in document order having meaning
help or
> hinder
> 	interoperability? What about understandability?
> 
> 	Thanks,
> 	Tim-
> 
> 	> -----Original Message-----
> 	> From: public-ws-addressing-request@w3.org
> 	> [mailto:public-ws-addressing-request@w3.org] On Behalf Of
> 	> paul.downey@bt.com
> 	> Sent: Wednesday, January 12, 2005 11:38 AM
> 	> To: noah_mendelsohn@us.ibm.com
> 	> Cc: public-ws-addressing@w3.org
> 	> Subject: RE: i009 - mustIgnore rule for multiple To, ReplyTo,
etc.
> 	>
> 	>
> 	> Noah,
> 	>
> 	> Thanks for your help, in particular the quotation from the
> 	> SOAP 1.2 Rec S2.6[1]. I'm assuming that a similar processing
> 	> model also applies to SOAP 1.1, though i couldn't find that
> 	> explicitly stated in the note or the WS-I Basic Profile. As
> 	> i'm sure you are aware, we are chartered to provide bindings
> 	> for both SOAP 1.1 and 1.2 and I believe it is desirable to
> 	> have the same mustIgnore rule for multiple EPRs applied to
> 	> both bindings.
> 	>
> 	> > I'm not recommending one approach or another for ReplyTo
> 	> and friends,
> 	> > but just pointing out that the SOAP recommendation provides
> 	> the option:
> 	> > if you want to say in the specification for some SOAP header
> block:
> 	> > "all occurrences of blocks with this QName must be processed
in
> 	> > document order", the SOAP Rec. says you can do that.
> 	>
> 	> That sounds good to me, assuming SOAP 1.1 has the same
> 	> processing model.
> 	>
> 	> > Now, whether most of the widely
> 	> > deployed implementations of SOAP make it easy to achieve
> 	> such control
> 	> > is a different question.
> 	>
> 	> Given we're writing a specification I would like to think we
> 	> can follow correctness here and specify a significance to the
> 	> order for repeated headers in the wsa namespace.
> 	>
> 	> >From a brief look at a couple of SOAP APIs taken at random it
> seems
> 	> that you can usually iterate through the SOAP headers in
> 	> order, though some tools which provide an application
> 	> binding, generating code for headers directly described in
> 	> WSDL will have difficulties.
> 	> Then again such an approach at implementing wsa will
> 	> encounter many other difficulties. Maybe this isn't such an
> 	> issue in practice after all.
> 	>
> 	> My remaining concern regards a use-case Don Box outlined at
> 	> our Redmond F2F in which other non-wsa components in a SOAP
> 	> processing pipeline may trigger off wsa headers, such as EPR
> 	> parameters and properties.
> 	> Such side-effects could be oblivious to our mustIgnore rule
> 	> if they encountered a repeated item, but then they would have
> 	> to consider other items being repeated anyway - i don't see
> 	> this as an issue.
> 	>
> 	> So I'm happy to rewrite the Option#3 proposal more concretely
> 	> to state 'subsequent unexpected wsa:Address, wsa:wsa:To,
> 	> wsa:ReplyTo, wsa:FaultTo items must be ignored", assuming
> 	> there's no strong disagreement from the WG on this direction?
> 	>
> 	> Paul
> 	>
> 	> [1] http://www.w3.org/TR/soap12-part1/#procsoapmsgs
> 	>
> 	>
> 
> 
> 
> 
>

Received on Wednesday, 12 January 2005 23:27:18 UTC