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Re: Describing which blobs are to be optimized.

From: David Booth <dbooth@w3.org>
Date: Fri, 23 Jul 2004 17:18:02 -0400
Message-Id: <5.1.0.14.2.20040722153952.0421ce98@localhost>
To: Marc Hadley <Marc.Hadley@Sun.COM>
Cc: www-ws-desc@w3.org, Glen Daniels <gdaniels@sonicsoftware.com>, Hugo Haas <hugo@w3.org>, Ugo Corda <UCorda@SeeBeyond.com>, xml-dist-app@w3.org, David Fallside <fallside@us.ibm.com>

Marc,

The WSD WG accepted[1] my proposed clarification[2], although as of this 
writing the editors have not yet incorporated this clarification into 
Section 8.3 of our draft document[3].

In essence, the clarification was:
[[
This means that if a WSD declares a feature to be optional (i.e., it
declares the feature but does not set wsdl:required=true), then a provider
agent implementing that WSD MUST NOT send a message that requires the
requester agent to support that feature, UNLESS the provider agent has some
other information -- beyond what is stated in the WSD -- that assures the
provider agent that the requester agent actually supports that
feature.  For example, in a request-response interaction, the requester
agent might provide such information by sending a message that includes a
flag indicating "by the way, I support feature X, so you may use that
feature when you send back your response".
]]

Let me know if you have further questions about this.


References
1. WG accepted proposed clarifications:
http://lists.w3.org/Archives/Public/www-ws-desc/2004Jun/0192.html
2. Proposed clarifications:
http://lists.w3.org/Archives/Public/www-ws-desc/2004Jun/0090.html
3. WSDL 2.0 Editor's draft:
http://dev.w3.org/cvsweb/~checkout~/2002/ws/desc/wsdl20/wsdl20.html?content-type=text/html;%20charset=utf-8#processor


At 06:06 PM 7/14/2004 -0400, Marc Hadley wrote:
>I took an action on this weeks XMLP telcon to enquire as to the
>resolution of the issue raised about the meaning of
>wsdl:required="false" on the proposed feature. Was this resolved and if
>so how ?
>
>Thanks,
>Marc.
>
>On Jun 11, 2004, at 5:54 PM, David Booth wrote:
>
>>
>>[Reposting because I forgot to copy xml-dist-app@w3.org.  Sorry!]
>>
>>Regarding the discussion about the meaning of an optional feature, I
>>think this issue is actually already addressed on our draft, and I
>>think the draft has it right, though it's possible we should add more
>>clarification.
>>
>>Section 8.3
>>http://dev.w3.org/cvsweb/~checkout~/2002/ws/desc/wsdl20/ 
>>wsdl20.html#processor
>>says "A conformant WSDL processor MAY safely ignore a NON-mandatory
>>extension that it does not recognize or that it does not choose to
>>implement." (and also clarifies that the conformant processor is
>>acting on behalf of the requester entity -- not the provider entity).
>>
>>This means that if a WSD declares a feature to be optional (i.e., it
>>declares the feature but does not set wsdl:required=true), then a
>>provider agent implementing that WSD MUST NOT send a message that
>>requires the requester agent to support that feature, UNLESS the
>>provider agent has some other information -- beyond what is stated in
>>the WSD -- that assures the provider agent that the requester agent
>>actually supports that feature.  For example, in a request-response
>>interaction, the requester agent might provide such information by
>>sending a message that includes a flag indicating "by the way, I
>>support feature X, so you may use that feature when you send back your
>>response".
>>
>>This is NOT a symmetric interpretation of "optional", for a very good
>>reason: The WSD identifies (and applies to) the particular provider
>>agent identified by the endpoint declaration.  But it does not
>>identify the requester agent.  It applies to *any* hypothetical
>>requester agent that engages the provider agent under this WSD.  The
>>WSD permits the provider agent to declare its own support for a
>>feature (which any requester agent may therefore use), but there is no
>>way in the WSD to declare what any particular requester agent ACTUALLY
>>supports.  It is only possible to declare a requirement of what the
>>(hypothetical) requester MUST support.
>>
>>>From: Hugo Haas <hugo@w3.org>
>>>Date: Mon, 7 Jun 2004 16:15:55 +0200
>>>. . .
>>>When the use of the MTOM feature is not required, it just means that
>>>the service supports it, which means that the requester agent or the
>>>provider agent may use it, depending on the direction of the message
>>>. . . .
>>
>>Careful.  As explained above, unless the provider agent has other
>>information to know that the requester agent actually supports the
>>feature, then the provider agent should not send the requester agent a
>>message that requires use of the feature.
>>
>>>From: Glen Daniels <gdaniels@sonicsoftware.com>
>>>Date: Mon, 7 Jun 2004 11:49:19 -0400
>>>
>>>. . . Second, we could add something like a "mustUnderstand"
>>>attribute to
>>>feature/module declarations, which indicates that anyone using the
>>>WSDL
>>>must understand the given extension, but that the usage of that
>>>extension is still optional unless "required='true'" is specified. .
>>>. .
>>
>>It sounds like you're suggesting a way to distinguish between
>>requiring the requester agent *accept* messages that use a particular
>>feature, versus requiring the requester agent to *send* messages using
>>a particular feature.
>>
>>I don't think we need to add anything to WSDL to gain this ability,
>>since it could be done by splitting feature X into two features,
>>X-input and X-output --- one pertaining to service input and the other
>>to service output:
>>         feature X-input means that feature X is used on service input
>>         feature X-output means that feature X is used on service output
>>
>>So on combining these two features with the two possible values of
>>wsdl:required, we get four cases:
>>
>>1. Declaring feature X-input with wsdl:required=false means that the
>>requester agent MAY send messages using feature X, and the provider
>>agent will understand them.
>>
>>2. Declaring feature X-input with wsdl:required=true means that the
>>requester agent MUST send messages using feature X, and the provider
>>agent will understand them.
>>
>>3. Declaring feature X-output with wsdl:required=false means that the
>>provider agent has the ABILITY to send messages using, but should not
>>do so without other information to know that the requester agent can
>>accept them.
>>
>>4. Declaring feature X-output with wsdl:required=true means that the
>>provider agent MUST be prepared to receive messages using feature X.
>>
>>
>>--
>>David Booth
>>W3C Fellow / Hewlett-Packard
>>Telephone: +1.617.253.1273
>>
>---
>Marc Hadley <marc.hadley at sun.com>
>Web Products, Technologies and Standards, Sun Microsystems.

-- 
David Booth
W3C Fellow / Hewlett-Packard
Telephone: +1.617.253.1273
Received on Friday, 23 July 2004 17:18:32 GMT

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