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Two logical WSDL documents describing the same service

From: David Booth <dbooth@w3.org>
Date: Wed, 17 Dec 2003 22:22:59 -0500
Message-Id: <5.1.0.14.2.20031217221638.03206b68@localhost>
To: www-ws-desc@w3.org

At the last WS Architecture F2F meeting, a question arose about whether the 
WSDL 2.0 specification has anything to say about a single service being 
described by two different WSDL documents.  I took an action to write to 
the WSD WG to ask.

The question arose in the context of discussing WS Management: A single 
service wishes to expose a functional interface for its regular users, but 
it also wishes to expose a management interface.  Since a Web service 
description (WSD) in WSDL 2.0 is not allowed to specify more than one 
wsdl:interface, one obvious approach would be to write two WSDL documents 
that define different interfaces -- a functional interface and a management 
interface -- but that specify exactly the same targetNamespace and service 
name, so they are describing the same service.  In fact, they might even 
specify the same endpoint address.

This problem may sound familiar, because it's exactly the problem that the 
proposed @targetResource attribute was intended to address.   But in this 
case it skips the additional attribute.

At present, our Part1 document says that you cannot have two interfaces for 
the same service.  HOWEVER, my understanding of the context of that is that 
it pertains only to a *single* logical WSDL document[1] -- not multiple 
logical WSDL documents.  (By "logical WSDL document" I mean the infoset or 
WSDL components obtained from a single WSDL document and any of its 
includes, imports, etc.  See [1] if you're unclear about what I mean 
.)  Since this issue of single versus multiple logical WSDL documents[1] 
has only recently been raised, I don't think we've addressed the question 
of multiple logical WSDL documents describing the same service in this context.

My own reasoning about this is as follows.
1. The WSDL 2.0 spec should only define the meaning of any *single* valid 
sentence in the language, i.e., only any *single* logical WSDL document.
2. Therefore, the WSDL 2.0 spec should have nothing to say about the 
meaning or validity of two logical WSDL documents (each independently 
valid) when considered together.
3. In the Web in general, it is entirely normal to have multiple documents 
that describe the same resource.  Each such document may add to your 
knowledge of that resource.  Furthermore, following an "open world 
assumption", you should never assume that you know *everything* about a 
particular resource.  The idea of having two WSDL documents that describe 
the same resource seems entirely consistent with this view.
4. Therefore, I see nothing wrong with using two logical WSDL documents to 
describe the same service, even if those documents specify different 
interfaces.  If someone wants to create a PrinterService whose 
PrintDocument interface is defined in one WSDL document, but whose 
ManagePrinter interface is defined in another WSDL document, they are free 
to do so.

Do others agree with this analysis?


1. http://lists.w3.org/Archives/Public/www-ws-desc/2003Nov/0085.html



-- 
David Booth
W3C Fellow / Hewlett-Packard
Telephone: +1.617.253.1273
Received on Wednesday, 17 December 2003 22:23:35 GMT

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