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Re: Comments on the pretty pictures

From: Arthur Ryman <ryman@ca.ibm.com>
Date: Thu, 12 Jun 2003 16:08:17 -0400
To: "Amelia A. Lewis" <alewis@tibco.com>
Cc: WS Description List <www-ws-desc@w3.org>, www-ws-desc-request@w3.org
Message-ID: <OFC6A354FA.9F125B99-ON85256D43.006C4A8F@torolab.ibm.com>

You wrote:

"The use of "resource" as a larger thing than "service" is a reversal of
common use.  Commonest-of-all use of "resource" is in the terms "uniform
resource locator" or "uniform resource identifier"; these terms
implicitly define a resource as being an endpoint and an interface; the
fact that multiple resources may point at the same abstract [something],
or share its state, indicates that the general use of the term
"resource" is to indicate a subset of an interface on a service."

Look at the following section of the WSDL 1.1 spec: 

"If a service has several ports that share a port type, but employ 
different bindings or addresses, the ports are alternatives. Each port 
provides semantically equivalent behavior (within the transport and 
message format limitations imposed by each binding). This allows a 
consumer of a WSDL document to choose particular port(s) to communicate 
with based on some criteria (protocol, distance, etc.)."

Each endpoint is a resource, but there is also another resource which 
represents the "equivalence class" of the endpoints. This other resource 
is conceptually useful since it abstracts out the details of the protocol.

For example, suppose a financial services company offers a Stock Quote 
service whose endpoint is http://www.finance.com/StockQuote. That's one 
endpoint. But after a while, some customers ask for a secure way to access 
the service, since they are worried there interests in certain stocks may 
be observed. The financial services company then makes the same function 
available at http://www.finance.com/StockQuote - same interface, same 
function, but different protocol. Now we have two endoints:

1. http://www.finance.com/StocKQuote
2. https://www.finance.com/StocKQuote

We have two endpoint resources, but just one target resource of the 
service. We can lump these in a single <service> element, and not 
explicitly name the target resource, or we can have separate <service> 
elements and related them via the @targetResource attribute.

Arthur Ryman
Received on Thursday, 12 June 2003 16:08:48 UTC

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