Minority Opinon re: Compositors [IONA, Oracle, Sonic, Sun]

At the Boston f2f meeting [1], five companies presented a proposal to
address composition of extensions [2] which was rejected in [3]. The
proposal specifies a general mechanism for composition of
extensibility within WSDL documents that include not only Features and
Properties, but also WSDL extensions.

This email constitutes the minority opinion of IONA Technologies,
Oracle Corporation, Sonic Software, and Sun Microsystems with respect
to the Web Services Description Working Group's decision of NOT
adopting the compositors proposal [2] taken at the Cannes F2F Meeting
in March 2004 [3].

In summary, it is our opinion that
(1) There is a genuine need to add simple composition of capabilities
    that are expressed with extension mechanisms in WSDL.  Not
    including composition of extensions in WSDL is a hindrance to
    interoperability of real world Web services.

(2) The WG did not give adequate technical consideration to a proposal
    which we believe is a good basis for a functional and flexible
    solution to (1).  This is an issue because a) other proposals
    introduced later received much more attention, and b) we believe
    the opposing companies pushed this discussion to a close based on
    a potential overlap with their proprietary work rather than
    technical merit or the needs of WSDL users.

Below we briefly discuss the details of the problem, the current
landscape of solutions and illustrate why this topic requires further
consideration within the wg.

1. Problem and Proposed Solution: 

The inclusion of Features and Properties (F&P) in the WSDL
specification shows that there is a genuine need to express the
capabilities and requirements of a Web Service. Adoption of F&P has
been confirmed by the working group in three separate votes, clearly
indicating the need for describing such capabilities, and validating
the work of the XML Protocol group in initiating this architecture.

The Choreography working group also expressed the necessity of this
feature within WSDL in [4]. Today, there is no standard mechanism for
expressing the composition of capabilities for Web Services.

Clients of a Web service use the WSDL document as the contract to
communicate with the Web service. The choices within a configuration
and the interdependencies between configurations and capabilities that
a Web service exposes are essential for a client's interaction with
the Web service.  Currently, the WSDL specification provides
mechanisms for including a set of optional or required extensions or
property values/constraints. Based on research and product
implementation experience of the companies that authored the proposal,
the composition and the expression of dependencies between individual
features, properties and/or extensions is an essential capability that
needs to be included in the WSDL specification, in addition to F&P.

Web services are increasingly being used for business-critical
applications. The industry is beyond looking at toy examples and is
now addressing extensions that need to be integrated with Web services
and configured accordingly. Clients of a Web service need to know when
to utilize a specific feature, such as security, and the
configurations that a Web Service permits or requires. For example,
the decision as to whether or not to have each request notarized by an
intermediary might be contingent on whether a security feature is in
use.  We believe these types of simple boolean compositions are going
to be commonplace, and that some language to express them needs to be
present in WSDL 2.0 in order to enable interoperable description of
large scale Web services exposing complex features such as security,
transactions, and reliable messaging.

The proposal [1] fills this important gap by providing a mechanism
that applies to all extension mechanisms in WSDL.

2. Compositors Discussion in the WSD WG

We believe that the decision of the WG not to move forward with the
compositors proposal is troublesome for the following reasons:

(a) The technical merits of the proposal were not adequately
discussed. There has been no email correspondance about either the
merits or the inadequacies of the proposal, thus making it impossible
to further develop and enhance the proposal to address any concerns
that wg members may have had.  There was only minimal discussion
during the Cannes f2f meeting. During said meeting [3], there were a
couple of enhancements/suggestions that were brought up by members of
the WG such as:

   -- limiting the levels of composition. 
   -- syntactic simplification.

These ideas were very amenable to the companies that authored the
compositor proposal; however the working group was not allowed to
develop these enhancements further since a decision about the proposal
was made before these suggestions could be explored.

(b) Given that there are no solutions based on open standards today,
the developers of Web services do not have any mechanism to express
composition in WSDL that ensures interoperability. This is our major
concern.  We understand that other proprietary specifications (in
particular WS-Policy [5,6,7]) attempt this same ground, and that the
W3C intends to hold a workshop in this area later this year [8].  We
strongly feel that waiting for a group to spin up and complete in this
area will "miss the boat", and that a simple solution covering the
80-20 case should be included in WSDL.

The compositors proposal, with a bit more work, could and should
become such a simple solution, and would allow Web service developers
to adequately describe more than just the required or optional status
of individual extensions.  We also feel that the existence of
proprietary work outside the WG was a primary (and inappropriate)
motivator for the early dismissal of the compositors effort.

(c) One of the arguments presented to the wg for not including the
proposal was the scope of the proposal and that it was late to enhance
the proposal during the course of the development.

However, the WG has been allowed to entertain other new proposals
after the f2f meeting which were not fully developed and have the
support of several member companies. Further, the WG was subjected to
longer discussion on proposals that were previously defeated but were
rediscussed at the f2f.  The compositor proposal did not get a second
hearing after its rejection although the authors of the proposal were
willing to accomodate the suggestions of the working group and
integrate them into the proposal if given the opportunity.

4. Conclusion: 

IONA Technologies, Oracle Corporation, Sonic Software, and Sun
Microsystems are committed to open standards that provide
interoperability.  WSDL needs a simple mechanism for describing not
only the extensions/capabilities associated with a Web service
(already present in the spec via extensions and F&P), but simple
boolean combinations which allow WSDL writers to express richer
compositions without modifying the extensions themselves.  It is our
opinion that the decision of the WG not to fully consider this work
was too quick, and made for the wrong reasons.

We request W3C to re-evaluate the process of reaching this
decision. We would like to see the simple composition of extensions
addressed by the WSDL WG as part of the WSDL 2.0 specification;
otherwise interoperability for real-world Web Services will remain an
elusive goal for "sometime in the future".

- Eric Newcomer (IONA Technologies)
- Umit Yalcinalp, Jeff Mischkinsky (Oracle Corporation)
- Glen Daniels (Sonic Software)
- Roberto Chinnici (Sun Microsystems)


[1] http://lists.w3.org/Archives/Public/www-ws-desc/2004Feb/0012.html
[2] http://lists.w3.org/Archives/Public/www-ws-desc/2004Jan/0153.html
[3] http://lists.w3.org/Archives/Public/www-ws-desc/2004Mar/0039.html
[4] http://lists.w3.org/Archives/Public/www-ws-desc/2004Jan/0066.html
[5] http://msdn.microsoft.com/ws/2002/12/Policy/
[6] http://msdn.microsoft.com/ws/2002/12/PolicyAssertions/
[7] http://msdn.microsoft.com/ws/2002/12/PolicyAttachment/
[8] http://www.w3.org/2004/06/ws-cc-cfp.html

Received on Thursday, 29 July 2004 08:50:32 UTC