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Re: targetResource wording

From: David Booth <dbooth@w3.org>
Date: Thu, 19 Jun 2003 15:14:02 -0400
Message-Id: <5.1.0.14.2.20030619115045.024edcf8@localhost>
To: www-ws-desc@w3.org
Cc: Mark Baker <distobj@acm.org>, "Sanjiva Weerawarana" <sanjiva@watson.ibm.com>, "Champion, Mike" <Mike.Champion@SoftwareAG-USA.com>

It looks to me like there is some misconception of what the targetResource 
means, partly (I think) because some of the statements in this discussion 
have been a little imprecise.

The targetResource attribute has nothing to do with describing a 
service.  It is used to indicate a relationship *between* services.  Its 
purpose is to allow two WSDL <service> descriptions, d1 and d2, to assert 
that (behind the scenes) the services s1 and s2 that they describe are 
actually "manipulating" the same resource.  In other words, if d1 and d2 
both state "targetResource='u'", where u is some URI, then they have 
asserted that s1 and s2 "manipulate" the resource r that is identified by 
URI u.

As we know from RFC2396[1], a resource can be anything -- a physical 
object, an abstract concept -- anything.  So what does it mean to say that 
s1 and s2 "manipulate" the same resource r?  Without knowing the semantics 
of d1 and d2 you don't know.  That is not defined by the WSDL 1.2 
specification.  (Nor should it be, IMO.)  Until you know the semantics of 
d1 and d2, the only concrete thing you can conclude is that s1 and s2 are 
somehow related to each other through r.

(Just in case there is confusion about this, the "targetResource='u'" 
attribute is NOT asserting that s1 and s2 are the same resource as each 
other, nor is it asserting that s1 and s2 are the same resource as r.)

Does this vagueness present a problem?  No.  Different applications will 
know what they wish to do with this.  (The canonical example is a 
printDocument service s1 and a managePrinter service s2, both manipulating 
the same physical printer r.)  The reason the WG described the 
targetResource as "manipulating" the same resource was to give users 
guidance about its intended use, even though the precise meaning of the 
word "manipulate" is impossible to nail down in this context.

Regarding the name "targetResource", u does identify a resource, so the 
"Resource" part of the name definitely is appropriate.  Furthermore, 
proponents of the targetResource attribute like to think of r as being the 
ultimate "target" of interactions with s1 or s2; hence the name 
"targetResource".

I hope this helps to clarify the situation.


1. RFC2396: http://www.ietf.org/rfc/rfc2396.txt


-- 
David Booth
W3C Fellow / Hewlett-Packard
Telephone: +1.617.253.1273
Received on Thursday, 19 June 2003 15:14:08 GMT

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