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Re: Behaviour of WS-Policy aware clients

From: Sergey Beryozkin <sergey.beryozkin@iona.com>
Date: Wed, 20 Sep 2006 09:48:44 +0100
Message-ID: <00e601c6dc91$94acf790$3901020a@sberyoz>
To: "Maryann Hondo" <mhondo@us.ibm.com>
Cc: <public-ws-policy@w3.org>, <public-ws-policy-request@w3.org>
Hi Maryann

Thanks for your answer.

The real motivation behind my question, especially behind the first one, is to understand what a requester
should do if it encounters a policy with a single alternative which contains a bunch of assertions with no wire manifestations.

Consider this example :

<wsp:Policy>
   <wsp:ExactlyOnce>
         <oasis:QOSGuarantee>
              <NeverFails/>
              <TheBestServiceInThisCategory verifiedBy="..."/>
         <oasis:QOSGuarantee>
   <wsp/ExactlyOnce>
<wsp:Policy>

A (requester) entity may use this policy in order to select this service among many other similar services.
The above oasis:QOSGuarantee policy assertion has no wire manifestations, it can be used by a requester for a proper services selection only. In other words, irrespectively of whether the (requester) entity fails to recognize this assertion or not, it can not affect the outcome of the communication with a given service as this assertion has no wire representations.

Hence the question :

* should a ws-policy aware (requester) entity fail if it can't support the above policy due to the fact its single alternative is not recognized. Note that oasis:QOSGuarantee may be a well-known policy expression but this given entity's runtime just is not aware of it yet.

Cheers, Sergey Beryozkin
Iona Technologies



  Sergey, 
  We're currently working on clarifying the text. 
  In the interim, I'll give you my opinion. 

  First of all, the goal of policy is to have assertions define the capabilities and constraints of an "entity" ( we are working on changing "requestor" and "provider" to "entity" with an e.g, requestor/provider) to enable interoperability of web services. 

  So, if a "provider" indicates a constraint ( let's assume its " all messages to me must be signed") and you don't know what that means, then chances are any attempt to send a message to the provider will fail.  If you're really, really lucky, and you always sign all your messages maybe you'll guess right on the algorithm and other metadata about signing, but its kind of a long shot. 

  For 2, again, the idea here is if you are the "provider of a service" you probably want people to get messages to you (othewise, why expose a service?). 
  If you support a whole bunch of options, but don't tell anyone about it, chances are a few people may try, but if they try and fail, not many people are going to keep trying to send you messages with every possible alternative configuration. 
  Maybe you have something that people can't live without and they're willing to try, try again, but I find there's a point at which they will move on to someone who is clear about their expectations thus increasing their chance of success.The intent of web services is to enable interoperability, if you want to hide why bother exposing your services? 

  In order to demonstrate interoperability there are some requirements: 

  A requester may choose any alternative since each is a valid configuration for interaction with the service, but a requester MUST choose only a single alternative for an interaction with a service since each represents an alternative configuration. 

  If an assertion in the normal form of a policy expression contains a nested policy expression, the nested policy expression MUST contain at most one policy alternative 

  but there is not currently normative text that I'm aware of that says "A client MUST not send a message" because I'm not sure how anyone would enforce this. 

  Maryann 




        "Sergey Beryozkin" <sergey.beryozkin@iona.com> 
        Sent by: public-ws-policy-request@w3.org 
        09/19/2006 12:29 PM 
       To "Sergey Beryozkin" <sergey.beryozkin@iona.com>, <public-ws-policy@w3.org>  
              cc  
              Subject Behaviour of WS-Policy aware clients 

              

       



  Hello 
    
  A couple of questions on the expected behaviour of a WS-Policy aware client. 
    
  1. Suppose we have a policy with a *single* alternative which a policy-aware client can not support 
  due to the fact it does not *recognize* its assertions (no intersection is involved). 
  Is it expected to fail ? Can it attempt to initiate a communication with the provider ? 
    
  1. Suppose we have a policy which a policy-aware client can not support 
  due to the fact an intersection produced an empty set. 
  Is it expected to fail ? Can it attempt to initiate a communication with the provider ? 
    
  Thanks, Sergey Beryozkin 
  Iona Technologies 
Received on Wednesday, 20 September 2006 08:47:48 GMT

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