Re: Policy expressions with no wire manifestation

Hi all,

After thinking a bit more about policies which express capabilities with no wire manifestations and no associated behaviours expected from a consumer of such policies, I came to some conclusion.

Here's an example :

wsp:Policy> 
   <wsp:ExactlyOnce> 
      <wsp:All>
         <!--- security assertion -->
         <sp:HttpsToken/>
      </wsp:All>
      <wsp:All> 
         <!-- capability assertion -->
         <oasis:QOSGuarantee> 
            <NeverEverFails/> 
         </oasis:QOSGuarantee> 
         <!--- security assertion -->
         <sp:HttpsToken/>
      </wsp:All>
   <wsp/ExactlyOnce> 
<wsp:Policy>

A policy designer wishes to tell to ws-policy aware entities out there that they must be able to use HTTPS should they attempt to start communicating with the service. 
Futhermore, a policy designer wishes to tell that the service has a well-known capability to never fail, but is careful to ensure that the entities not aware of what this means but still meeting a key requirement of being able to use HTTPS can still enjoy communicating with this service. A policy author achives this by creating two policy alternatives. 
The reason is simple : <oasis:QOSGuarantee> assertion is not a requirement but a capability which has no wire manifestations and behavioural requirements for the entities which can understand what it means.

In fact, the above expression, being in a normal form, is equivalent to this compact expression :

wsp:Policy> 
   <wsp:ExactlyOnce>  
       <sp:HttpsToken/>
        <oasis:QOSGuarantee wsp:optional="true"> 
            <NeverEverFails/> 
         </oasis:QOSGuarantee> 
   <wsp/ExactlyOnce> 
<wsp:Policy>

Making such policy assertion as <oasis:QOSGuarantee>  would unnecessarily limit the audience of this service. A requester entity should never fail if it does not understand what <oasis:QOSGuarantee>  given the fact the only thing it can ever do with it is to note that this service posesses the advertised quality and see whether it meets its selection criteria or not.

For example, if a requester searches for services which are known to publish its message logging traces to a well known external site it shoud be sufficient for it to be able to recognize a well known <common:publishTraces href="..."/> rather than fail due to the fact <oasis:QOSGuarantee/>  is not recognized. Likewise those searching for never failing services should be able to consume those who assert it and not fail should they not recognize <common:publishTraces href="..."/>.

This brings me to a simple conclusion : Policy authors SHOULD be encouraged to use wsp:optional when using policy asssertions which advertise capabilities with no associated behavioral requirements and wire representations in order to widen the service's audience and improve interoperability. wsp:optional means here that it's a capability which *may* be used for a service selection. I believe guidelined for policy authors should be updated.

At the moment the WS-Policy Framework (primer) uses wsp:optional to mark assertions which identify behaviours which *may* be engaged. It refers to such assertions as 'capabilities'. IMHO it's not the best/too broad the definition and it will cause confusions. For ex : <mtom:OptimizedMimeSerialization wsp:optional="true"/>. I feel it's better be additionally categorised as an optional requirement. 

Any thoughts or objections ?

Likewise an assertion like <sp:MustSupportRefKeyIdentifier />  does not fall into this category because a policy author *requires* a consuming entity to understand it, ortherwise the secure processing on either side will fail.

Thanks, Sergey Beryozkin
Iona Technologies



  It is my understanding that people are using the wsp:optional to handle this. So if the requester (consumer) doesn't know about it they can ignore it. 


  This works BUT it is really using wsp:optional in an unintended way. The truth is that such an assertion is not really optional it's only optional in the sense that the requester can ignore it however the provider must be providing this level of service and the requester must do nothing - so in that sense it really isn't optional it's just a handy use of the wsp:optional.


  This is one of the reasons I think there could be another attribute missing (like the wsp:local).


  Another reason for having such an attribute would be for the generic engine to be able to handle such a thing consistently in all implementations. e.g. if I had a wh:local then I'd be forcing the requester to either know about my namespace or assume that they can't use this service. I think it can just make things messier than they need to be.


  Having said all that I understand the effort that introducing a new attribute would mean and seeing as you can get a similar affect using things like wsp:optional (albeit in an unintended way) I expect push back on the idea.


  Regards,
  William


  On Sep 20, 2006, at 11:46 AM, Beryozkin, Sergey wrote:


    Hi Maryann, others

    this is most helpful...

    "I would note that if you're "using the assertion for selection", it could 
    imply that you know what it is."

    Ok, I think I start understanding it (fingers crossed :-)). A requester runtime may be required to select services which are highly available. It expects providers to advertize well-known <oasis:HighlyAvailable/> assertions. If a provider advertizes a policy which have no <oasis:HighlyAvailable/> assertions then the intersection will fail. I think it's reasonable.

    Now consider a different case.
    A requester runtime has no priori policy requirements. However it understands all well-known security assertions but no others ones. It has found a service which requires that a requester supports some security policies.

    Futhermore, a provider wishes to advertize some of its capabilities, namely that it's the best service around. A requester does not know yet about such assertions and is not even planning to use assertions like this for services selection.

    How would we do it ?

    Like this  ? :

    <wsp:Policy> 
       <wsp:ExactlyOnce> 
          <wsp:All>
             <!--- security assertion -->
             <sp:HttpsToken/>
          </wsp:All>
          <wsp:All>
             <!-- capability assertion -->
             <oasis:QOSGuarantee> 
                <TheBestServiceInThisCategory verifiedBy="..."/> 
             </oasis:QOSGuarantee> 
             <!--- security assertion -->
             <sp:HttpsToken/>
          </wsp:All>
       <wsp/ExactlyOnce> 
    <wsp:Policy>

    Thanks,
    Sergey Beryozkin
    Iona Technologies

      ----- Original Message -----
      From: Maryann Hondo
      To: Sergey Beryozkin
      Cc: Anthony Nadalin ; public-ws-policy@w3.org ; public-ws-policy-request@w3.org ; Sergey Beryozkin
      Sent: Wednesday, September 20, 2006 2:17 PM
      Subject: Re: Policy expressions with no wire manifestation



      Sergey, 
      I responded to your other mail ...so this is a bit of a repetition. 

      In the guidelines document, Umit and I have attempted to capture "observations" about the use of optional, and this might 
      be a case where it would be useful.  I would note that if you're "using the assertion for selection", it could 
      imply that you know what it is. Whether or not it is required on the wire is a facet of the behavior associated with the assertion. 
      Each set of authors is given a set of tools by the specifications, but the authors need to craft the assertions. 

      Maryann 



            "Sergey Beryozkin" <sergey.beryozkin@iona.com> 
            Sent by: public-ws-policy-request@w3.org
            09/20/2006 05:35 AM
           To "Sergey Beryozkin" <sergey.beryozkin@iona.com>, Anthony Nadalin/Austin/IBM@IBMUS 
                  cc <public-ws-policy@w3.org>, <public-ws-policy-request@w3.org> 
                  Subject Re: Policy expressions with no wire manifestation 

                  

           



      Hi there 
        
      That was a response in a hurry so I take it back. Before flooding the group concalls with trivial issues I'd rather attempt to make my question as clear as possible. Note that I may indeed be confused, but if so then I'd appreciate an answer which would help. 
        
      Consider this example : 
        
      <wsp:Policy> 
         <wsp:ExactlyOnce> 
               <oasis:QOSGuarantee> 
                    <NeverFails/> 
                    <TheBestServiceInThisCategory verifiedBy="..."/> 
               <oasis:QOSGuarantee> 
         <wsp/ExactlyOnce> 
      <wsp:Policy> 
        
      This is an example of a policy with a single alternative. This alternative contains non-optional assertions 
      defined by a policy profile spec published a month ago. These assertions have no wire manifestations. 
      A ws-policy aware (requester) entity whose runtime has not been updated yet to recognize <oasis:QOSGuarantee> is about to start communicating with the service which advertizes this policy. 
        
      Given the fact that it's likely ws-policy aware requesters will refuse to start talking to a service should they fail to support the above policy and that the fact whether this requester supports this policy or not will have no effect on the actual communication with the service this policy attached to, my understanding is that such assertions with no wire manifestations SHOULD be marked as wsp:optional : 
        
      <wsp:Policy> 
         <wsp:ExactlyOnce> 
               <oasis:QOSGuarantee wsp:optional="true"> 
                    <!-- --> 
               <oasis:QOSGuarantee> 
         <wsp/ExactlyOnce> 
      <wsp:Policy> 
        
      This means a requester may use this policy for a service selection but doesn't need to refuse talking to this service should it fail to recognize the policy. 
        
      Does it make sense ? 
      What is the group's position on this issue ? 
        
      Thanks 
        
      Sergey Beryozkin 
      Iona Technologies