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RDDL (was Re: Definition for a Web Service)

From: Paul Denning <pauld@mitre.org>
Date: Thu, 14 Aug 2003 17:36:05 -0400
Message-Id: <5.2.0.9.0.20030814154746.0337e488@129.83.20.110>
To: "Sanjiva Weerawarana" <sanjiva@watson.ibm.com>
Cc: "Www-Ws-Arch@W3. Org" <www-ws-arch@w3.org>

At 12:44 PM 2003-08-12, Sanjiva Weerawarana wrote:
>Again, the QName of the <service> element is precisely the identity
>you are looking for IMO.
>
>Now, for a variety of reasons (including the fact that QNames are a
>PITA to write down), it is indeed useful to have a URI instead of a
>QName to identify things.

Thanks for your explanation of the QName stuff as it relates to WSDL.

I agree audit logs are important.

As you suggest, its nice to have a URI instead of a QName.

If you don't know anything about the URI, copy and paste into your browser 
to see what comes back.

This is similar to the TAG namespaceDocument-8 [1].

So if I have an audit log, with a URI that identifies the service (perhaps 
derived from the QName in some "standard" way), I may want to take that URI 
and learn more about the service it identifies.  Very similar to the 
namespace URI.

So if doing HTTP GET on a namespace URI returns a "namespace document", the 
HTTP GET on a web service URI should return a "web service document" (perhaps).

But the TAG seems to prefer RDDL [3] or RDF over directly returning an XSD 
document, since there may be other metadata documents besides an XSD.  TAG 
also says [2]
    * Having a document at the end of a namespace URI is good.
    * It's good if those documents are human-readable.
    * Indirection is useful in those documents. Point out the ability of 
RDDL to carry indirection..
    * There is some risk involved if you bet on some format for such 
documents as being the One and Only Format.
So, to extend this reasoning to web services, we might want to consider 
using RDDL as one suitable representation to return when dereferencing a 
web service URI.
Then we can have the following RDDL snippet as an example:

...
<a rddl:nature="http://www.w3.org/2003/06/wsdl" 
rddl:purpose="http://www.rddl.org/purposes#definition" 
href="...URI-of-WSDL-file">WSDL description</a>
<a rddl:nature="http://www.daml.org/services/owl-s/0.9/Service.owl" 
rddl:purpose="http://www.rddl.org/purposes#definition" 
href="...URI-of-OWL-S description">OWL-S description</a>
...

If the web service is identified as a QName (without a "standard" mapping 
to a URI), then we lose the ability to retrieve metadata about the service 
(in a manner consistent with the Web Architecture).

[1] http://www.w3.org/2001/tag/ilist#namespaceDocument-8
[2] http://www.w3.org/2003/07/21-tag-summary.html
[3] http://www.tbray.org/tag/rddl/rddl3.html

Paul 
Received on Thursday, 14 August 2003 17:36:16 GMT

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