WSDL-S's action and related WS-Addressing and WSDL discussions and concepts

Hi Meenakshi, Amit, and other SWS enthusiasts.

First, I decided to send my comments about WSDL-S's action
(originating from the Innsbruck workshop) to W3C's SWSIG list rather
than using the WSDL-S forum as I thought that I would reach a larger
number of interested parties by email, especially those present at the
workshop.

During the workshop on frameworks for semantics in Web services, it
was presented WSDL-S's idea of action which ties a WSDL operation to
an ontology.

I pointed out that this was interesting as similar discussions
happened and concepts existed in "traditional" (i.e. non-semantic) Web
services specifications.

I wanted to go over those in written form to start some discussion,
and hopefully manage to align people's minds on this topic.

WSDL-S defines an action property to be added to the WSDL operation
component. Interestingly, an action property was discussed for
addition in WSDL 2.0 recently. The proposal is at [1], and the
discussion at [2]. The Working Group didn't end up adopting it,
leaving it to other specification to do the work (including
WS-Addressing, see below), but I believe that the idea was the same in
both cases, coming from different angles.

As presented by David Booth in another WSDWG face-to-face meeting[3],
some of us believe that messages should be self-describing, and that
their meaning should be:
1. carried in them
2. described in a WSDL description

The name of action was used for two reasons:
- the old concept of SOAPAction started talking about "intent of the
  SOAP HTTP request"[4].
- similarly, WS-Addressing 1.0 has an action property "uniquely
  [identifying] the semantics implied by this message"[5]; this means
  that the action (a.k.a. verb, meaning, intent) appears in every
  message using addressing, contributing to the idea of
  self-describing messages.

WS-Addressing's action is an IRI, but the only direction given in the
spec about its value is a defaulting mechanism based on the WSDL
description[6]. This was the same algorithm which was proposed for
inclusion in WSDL 2.0[1], thinking that this concept of message
semantics was important enough to be added to WSDL 2.0's core.

WSDL-S's action provides a nice, low-cost bridge from Web services to
the Semantic Web, by actually defining useful values that action can
take, other than the simple WSDL defaulting algorithm.

The main difference is that WSDL-S has it at the operation level,
whereas discussions in the Web services worlds have let to the
conclusion that it should be a message level property.

If described with @wsa:Action[7] in WSDL 2.0, then WSDL-S's action (if
defined at the message level) would be nicely integrated on top of
core Web services specifications. I think that the description may not
necessarily be limited to using @wsa:Action, as it would tie it to
WS-Addressing 1.0 only, but this is interesting to consider.

So I would suggest WSDL-S authors to consider placing action at the
message level, and encourage them to have discussions with WS folks.

Regards,

Hugo

  1. http://lists.w3.org/Archives/Public/www-ws-desc/2005Feb/0035.html
  2. http://lists.w3.org/Archives/Public/www-ws-desc/2005Jun/att-0002/20050531-ws-desc-minutes.html#item02
  3. http://www.w3.org/2004/Talks/1110-dbooth-opname/slide25-0.html
  4. http://www.w3.org/TR/2000/NOTE-SOAP-20000508/#_Toc478383528
  5. http://www.w3.org/TR/2005/WD-ws-addr-core-20050331/#msgaddrprops
  6. http://www.w3.org/2002/ws/addr/5/04/wd/WD-ws-addr-wsdl-20050413/#defactionwsdl20
  7. http://www.w3.org/2002/ws/addr/5/04/wd/WD-ws-addr-wsdl-20050413/#explicitaction
-- 
Hugo Haas - W3C
mailto:hugo@w3.org - http://www.w3.org/People/Hugo/