Message adressing, intermediaries, and their description

Following up on my message about envelope and destination address[321]
which is I think only one part of the issue described below, which
also relates to issue 2[322], I have tried to capture my thoughts
underneath.

Sorry, they aren't very well structured, but I wanted to get those out
before I disappear for a couple of weeks to get the ball rolling. The
intermediary part is definitely related to MikeM's and MikeC's ongoing
work. Hopefully, this email will go in the same direction.

I think that we should have intermediaries on the face-to-face
agenda.

Mismatch between our document and SOAP 1.2:

- Our documents says that a message envelope contains address
  information to deliver the message.

- A SOAP message, and therefore a SOAP envelope, does not contain such
  information. It assumes that this information is known, either out
  of band, or using an extension.

- In a SOAP message, SOAP nodes are addressed with URIs which
  represent their roles. This role is not, in the general case, the
  address of a SOAP node, but an abstract name: e.g.
  "http://www.w3.org/2003/05/soap-envelope/role/next" is the next SOAP
  node receiving the message.

Description of services and intermediaries:

[ Note that I haven't reread carefully the WSDL 1.2 specification
  recently, so some of the things below may be wrong. Please correct
  anything which is incorrect in light of discussions in this group. ]

- Our service description concept discusses the description of a Web
  service's interface. The description of intermediaries is left out
  of the picture.

- As it currently stands, WSDL 1.2 leaves out intermediaries other
  than talking about the role attribute in the SOAP binding.

- One can wonder the role of the intermediaries in the architecture:
  - they are visible, addressable agents (which is certainly what SOAP
    1.2 is aiming at, I think): in this case, it may make sense to
    have them appear in the WSDL 1.2 abstract model, not just in the
    SOAP 1.2 binding; one way to see this is to have intermediaries
    described as services and have a role identifier specified, and
    then reference from other service descriptions.
  - they are just a SOAP artifact: I know that we have talked at the
    face-to-face meeting about talking about SOAP intermediaries as
    being Web services intermediaries; yet, I think that this makes
    them first-class objects.

What I think we need to do:

- In the message model, have an actor concept, which has a role
  identified by a URI; have headers targeted to actors; say something
  about the addressing (URL of a node) versus the targeting (URI of
  a role that a node acts at).

- We need to figure out what kind of description of intermediaries is
  necessary, and I think that we will need to talk to the WSDWG about
  this, as they probably had discussions of this kind before.

I hope that this is clear and on target enough.

Regards,

Hugo

  321. http://lists.w3.org/Archives/Public/www-ws-arch/2003Sep/0051.html
  322. http://www.w3.org/2002/ws/arch/2/issues/wsa-issues.html#x2
-- 
Hugo Haas - W3C
mailto:hugo@w3.org - http://www.w3.org/People/Hugo/