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RE: Proposal for R120 WSDL URI References

From: <ryman@ca.ibm.com>
Date: Thu, 31 Oct 2002 17:29:24 -0500
To: www-ws-desc@w3.org
Message-ID: <OFA3623DF9.993A2FDF-ON85256C63.0077C659@torolab.ibm.com>

David,

The fragment syntax I proposed is conformant with the XPointer Framework.
That framework reserves all schemes associated with application/xml, so in
order for us to define new schemes, we also need to define a new media
type, i.e. application/wsdl+xml. The WSD WG is checking with the TAG for
the official position wrt new media types.

Using raw XPointers is awkward for the reasons described by Eric [1], which
include:

1. an application would have to include an XPointer processor
2. XPointer syntax is very verbose
3. XPointers are not unique (e.g. you could use positional information
instead of attribute value matching). You would therefore have to define a
canonical form in order to simplify comparing WSDL URI-references.

Here's a simple example of how verbose XPointer is. Suppose portType "a"
contains operation "b" which has fault "c". The proposed fragement is:

#fault(a/b/c)

The XPointer fragment is:

#xmlns(w=http://schemas.xmlsoap.org/wsdl/) xpointer(//w:portType[@name
="a"]/w:operation[@name="b"]/w:fault[@name="c"])

I claim that this is 1) hard to write and, 2) hard to read.

Concerning the urn:wsdl: idea, the WSD WG agrees that it is not necessary.
The fragment identifier can be used with the target namespace-URI to
satisfy R120. I'll post an amended proposal soon. The context in which the
URI is used will define its interprettation (URL vs namespace-URI).

Concerning the treatment of extensibility elements, the creator of the
extension should define which ones need to be identifiable via
URI-references and then define an appropriate XPointer scheme, or specify
that full XPointer must be used. The base WSDL processing rules should
specify that additional extension schemes are allowed. I agree that the
proposal needs to be clear on how extension schemes are defined (e.g. to
manage scheme names to avoid collisions).

[1] http://lists.w3.org/Archives/Public/www-ws-desc/2002Sep/0082.html

Arthur Ryman


                                                                                                                                                    
                      "David Orchard"                                                                                                               
                      <dorchard@bea.com        To:       Arthur Ryman/Toronto/IBM@IBMCA, <www-ws-desc@w3.org>                                       
                      >                        cc:                                                                                                  
                      Sent by:                 Subject:  RE: Proposal for R120 WSDL URI References                                                  
                      www-ws-desc-reque                                                                                                             
                      st@w3.org                                                                                                                     
                                                                                                                                                    
                                                                                                                                                    
                      10/24/2002 06:23                                                                                                              
                      PM                                                                                                                            
                                                                                                                                                    
                                                                                                                                                    




Arthur et al,

I'm quite concerned about creating a new urn scheme and a media type and a
media type specific query/path syntax in order to get usable identifiers.
If yet another language has to create a frag id syntax/query language and
identifier syntax, I'd probably like to raise this as TAG issue, as there's
something clearly architecturally wrong.  grumble grumble.

Could you show syntax on why using URIs with XPointer and/or the XPointer
framework is so broken?

I agree that the use of http schemed URIs is confusing when the intent is
for identification.  But is foisting a domain name into a URN the best
solution?  There's been a great deal of discussion on this topic at the TAG
BTW.  I had proposed the use of an id: scheme (and larry masinter pointed
to
his tdb and duri schemes) that allow us to avoid specifying an http scheme
for non-dereferencable resources.  I had basically given up on pushing this
topic any further at the TAG because of lack of support (how many arguments
does one want?), but this might be a reason for it.

Is the url to urn mapping intended to be by-directional?  As in, can I take
a wsdl urn and construct a url from it?

I notice that you didn't show any extensibility elements, like soap or http
bindings.  Are they intended to be addressible?  How does an identifier of
an extensibility element in a different namespace get specified?

BTW, I was chortling as I thought through the use of the "name" attribute.
All the names in your sample document are intended to be unique within each
elements containment hierarchy.  So I got thinking about the way that HTML
used name attributes instead of id attributes <a name="foo"/> and #foo just
works.  We're almost back to html's use of names instead of ids.  If we
just
had an identifier type that was relative and a simple bare name query that
understood paths, I think most of your problems would be solved.
urn:wsdl:http://airline.wsdl/ticketagent/#message(listFlightsRequest) ->
urn:wsdl:http://airline.wsdl/ticketagent/#listFlightsRequest.  I do admit
that you've added types to your queries.

I'd also like to encourage y'all to think about these problems from an
overall web architecture perspective.  If the problems you are facing seem
more general than describing web services - like creating schemes and media
types in order to do identifier syntax? - then you might be able to punt
the
problem somewhere else.  The benefit is that you might have to do less
work.

Cheers,
Dave

> -----Original Message-----
> From: www-ws-desc-request@w3.org [mailto:www-ws-desc-request@w3.org]On
> Behalf Of ryman@ca.ibm.com
> Sent: Thursday, October 17, 2002 8:07 AM
> To: www-ws-desc@w3.org
> Subject: Proposal for R120 WSDL URI References
>
>
> Here's the proposal: (See attached file: URI-References.html)
>
> Arthur Ryman
Received on Thursday, 31 October 2002 17:30:04 GMT

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