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RE: NEW ISSUE: "Policy Alternatives" and "Policy" need proper def inition

From: Asir Vedamuthu <asirveda@microsoft.com>
Date: Wed, 2 Aug 2006 14:09:25 -0700
Message-ID: <4DF3D07B9910264B9470DA1F811D1A950B061AA3@RED-MSG-43.redmond.corp.microsoft.com>
To: "Asir Vedamuthu" <asirveda@microsoft.com>, "Prasad Yendluri" <prasad.yendluri@webmethods.com>, "Daniel Roth" <daniel.roth@microsoft.com>, <public-ws-policy@w3.org>
In the example below, it is not clear to me where assertions start and end. As described in Section 4.3.2 [1], a nested policy expression is a policy expression that is a child element of a policy assertion element:

"Any policy assertion MAY contain a nested policy expression. The schema outline for a nested policy expression is:

<Assertion …>
  …
  ( <wsp:Policy …> … </wsp:Policy> )?
  …
</Assertion>"

In the example below, it does not look like any of these assertions have nested policy expressions. Was this intentional? The normative text in Section 4.3.2 seems to be clear that this must be the case.

[1] http://www.w3.org/TR/2006/WD-ws-policy-20060731/#Policy_Assertion_Nesting


Regards,
 
Asir S Vedamuthu
Microsoft Corporation

________________________________________
From: public-ws-policy-request@w3.org [mailto:public-ws-policy-request@w3.org] On Behalf Of Asir Vedamuthu
Sent: Wednesday, August 02, 2006 7:12 AM
To: Prasad Yendluri; Daniel Roth; public-ws-policy@w3.org
Subject: RE: NEW ISSUE: "Policy Alternatives" and "Policy" need proper def inition

RE the text of the specification is not explicit enough for this

A full worked out example that demonstrates how the current definitions are ambiguous or not explicit enough is the best way to move forward on this.

Regards,
 
Asir S Vedamuthu
Microsoft Corporation

________________________________________
From: Prasad Yendluri [mailto:prasad.yendluri@webmethods.com] 
Sent: Tuesday, August 01, 2006 5:36 PM
To: Asir Vedamuthu; Prasad Yendluri; Daniel Roth; public-ws-policy@w3.org
Subject: RE: NEW ISSUE: "Policy Alternatives" and "Policy" need proper def inition

Hi Asir,

> I noticed that your example policies do not use any nested policy expression.

Section 4.3.3 defines:

Equivalence 
wsp:Policy is equivalent to wsp:All 

So, for readability, I have not explicitly put wsp:policy brackets around things and used wsp:All.

If my  examples have been, 

 Example Policy 1:

 <wsp:All> 
   <!-- assertion 5 --> 
   <wsp:ExactlyOne>     
          <!-- assertion 6 --> 
          <!-- assertion 7 -->
   </wsp:ExactlyOne>
  </wsp:All>

Example Policy 2:

<wsp:All>
  <wsp:ExactlyOne>  
    <!-- assertion 1 -->
    <!-- assertion 2 -->
  </wsp:ExactlyOne>
  <wsp:ExactlyOne>  
    <!-- assertion 4 -->
     . . . .
     <wsp:policy> 
        <!-- assertion 5 -->  
        <wsp:ExactlyOne>   
          <!-- assertion 6 --> 
          <!-- assertion 7 -->
       </wsp:ExactlyOne>
    </wsp:policy>
    . .  .  .
  </wsp:ExactlyOne>
</wsp:All>

Would you not then have the same policy alternates for Policy 1 and the nested policy in policy 2?
I understand the way you came up with the production of the alternatives for each policy and agree that is the correct way to arrive at them.  The point of the issue however is that, the text of the specification is not explicit enough for this. What makes a nested alternative in a Policy specification not an alternative of the parent policy, when policy is only defined to be “a collection of policy alternatives”? The nested policy and hence the embedded alternative is part of the same “collection” is it not?

Regards,
Prasad

-----Original Message-----
From: public-ws-policy-request@w3.org [mailto:public-ws-policy-request@w3.org] On Behalf Of Asir Vedamuthu
Sent: Tuesday, August 01, 2006 5:05 PM
To: Prasad Yendluri; Daniel Roth; public-ws-policy@w3.org
Subject: RE: NEW ISSUE: "Policy Alternatives" and "Policy" need proper def inition

Hi Prasad,

Thank you for writing down these examples. Let us look at the two policy expressions in your e-mail below.

Policy 1 has two alternatives:
A1 = {assertion 6, assertion 8}
A2 = {assertion 7, assertion 8} 

Policy 2 has six alternatives:
A3 = {assertion 1, assertion 4}
A4 = {assertion 2, assertion 4}
A5 = {assertion 1, assertion 5, assertion 6}
A6 = {assertion 1, assertion 5, assertion 7}
A7 = {assertion 2, assertion 5, assertion 6}
A8 = {assertion 2, assertion 5, assertion 7}
 
Two policy alternatives are compatible if each policy assertion in one alternative is compatible with a policy assertion in the other and vice-versa. None of the above policy alternatives are compatible. 

Two policies are compatible if a policy alternative in one is compatible with a policy alternative in the other. Policy 1 and Policy 2 are incompatible because none of the policy alternatives in Policy 1 is compatible with a policy alternative in Policy 2.

Just as expected, these two policies are incompatible. I noticed that your example policies do not use any nested policy expression.

I hope this helps.

PS: I’ll update your entry in Bugzilla.

Regards,
 
Asir S Vedamuthu
Microsoft Corporation

________________________________________
From: public-ws-policy-request@w3.org [mailto:public-ws-policy-request@w3.org] On Behalf Of Prasad Yendluri
Sent: Monday, July 31, 2006 5:32 PM
To: Daniel Roth; Prasad Yendluri; public-ws-policy@w3.org
Subject: RE: NEW ISSUE: "Policy Alternatives" and "Policy" need proper def inition

Dan,

Policy is defined to be a “collection of policy alternatives” only. Since an assertion in policy alternative can embed another policy (as defined below), a policy can end-up with policy alternatives in the policy embedded (in an assertion of an alternative).

   <Assertion …>
  …
  ( <wsp:Policy …> … </wsp:Policy> )?
  …
</Assertion>

There is generally no ambiguity until we run into further specifications that state things like “Two policies are compatible if an alternative in one is compatible with an alternative in the other.”

Suppose you have the following two Policy specifications:

            Example Policy 1:

 <wsp:All> 
   <wsp:ExactlyOne>      <!—Alternative A →
          <!-- assertion 6 --> 
          <!-- assertion 7 -->
   </wsp:ExactlyOne>
   <!-- assertion 8 -->  <!—Alternative B →
</wsp:All>

               Example Policy 2:

<wsp:All>
  <wsp:ExactlyOne>  <!—Alternative 1 Top level →
    <!-- assertion 1 -->
    <!-- assertion 2 -->
  </wsp:ExactlyOne>
  <wsp:ExactlyOne>  <!—Alternative 2 Top level →
    <!-- assertion 4 -->
    <wsp:All> 
        <!-- assertion 5 -->  <!—Alternative 3 Nested →
        <wsp:ExactlyOne>      <!—Alternative 4 Nested →
          <!-- assertion 6 --> 
          <!-- assertion 7 -->
       </wsp:ExactlyOne>
    </wsp:All>
  </wsp:ExactlyOne>
</wsp:All>


Turns out <!—Alternative A → in Example Policy 1 is compatible with (same definition as) the “nested” policy alternative marked 
<!—Alternative 4 Nested → in Example Policy 2.

Then using the definition, “Two policies are compatible if an alternative in one is compatible with an alternative in the other.”, one can conclude that Example Policy 1 and Example Policy 2 are compatible, without further qualification of “alternative in a policy”. In reality, the policies are not compatible of course even though, based purely on the current definition of policy (and other related entities), one can arrive at that conclusion.

Hope that clarifies the issue.

Regards,
Prasad

________________________________________
From: public-ws-policy-request@w3.org [mailto:public-ws-policy-request@w3.org] On Behalf Of Daniel Roth
Sent: Monday, July 31, 2006 4:24 PM
To: Prasad Yendluri; public-ws-policy@w3.org
Subject: RE: NEW ISSUE: "Policy Alternatives" and "Policy" need proper definit ion

I’m having difficulty understanding this issue.  Some examples that demonstrate how the current definitions are ambiguous would be helpful.

Thanks.

Daniel Roth

________________________________________
From: public-ws-policy-request@w3.org [mailto:public-ws-policy-request@w3.org] On Behalf Of Prasad Yendluri
Sent: Wednesday, July 26, 2006 4:15 PM
To: public-ws-policy@w3.org
Subject: NEW ISSUE: "Policy Alternatives" and "Policy" need proper definit ion

Title: "Policy Alternatives" and "Policy" need proper definition
 
Description: Section 2.3 terminology defines a “policy” to be, “a collection of policy alternatives”
No further constraints on how these alternatives are grouped, i.e. on the origin of alternatives in the collection.

Similarly section 3.2 (Policy) defines a “policy” to be: “a policy is a potentially empty collection of policy alternatives.”

This “collection” does not account for level of nesting of a specific policy alternative. 

Section 2.3 terminology defines a “Policy Alternative” to be “a collection of policy assertions” only. 
No further restriction on how these assertions are grouped (or) the origin of the assertions in the collection.


Similarly section 3.2 (Policy Alternative) defines a policy alternative to be: 
“A policy alternative is a logical construct which represents a potentially empty collection of policy assertions. An alternative with zero assertions indicates no behaviors.”

This “collection” again does not account for level of nesting of a policy assertion included.

Justification:
There is scope for interpretation that needs to be eliminated. “policy assertion” and “policy” definitions need to account for level of nesting of the collection they define. 
 
Target: WS-Policy 1.5 - Framework
 
Proposal – Tighten up the definitions of “policy” and “policy assertion”. Sorry I have not come up suggestion for a specific replacement text at this point.
Hope to follow-up later.


Regards,
Prasad Yendluri

Received on Wednesday, 2 August 2006 21:09:58 UTC

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