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Re: [Bug 4555] Should policy intersection be called policy intersection?

From: David Hull <dmh@tibco.com>
Date: Wed, 23 May 2007 12:47:02 -0400
Message-ID: <46547006.8020909@tibco.com>
To: Ashok Malhotra <ashok.malhotra@oracle.com>
CC: Asir Vedamuthu <asirveda@microsoft.com>, Paul Cotton <Paul.Cotton@microsoft.com>, "public-ws-policy@w3.org" <public-ws-policy@w3.org>
I missed this earlier in my mailbox.

If duplicate assertions are removed then, in the case where compatible
alternatives always have the same assertions, you have something quite a
bit like set intersection.  Even then, if alternatives can be compatible
without having exactly the same assertions, you will generally get back
some alternatives that don't occur in either policy, which is stretching
the notion of "intersection", particularly since the "intersection" can
end up with more alternatives than either of the two intersected
policies (e.g. {[A A B] [A B]} intersected with {[A A B] [A B B]} yields
{[A A A A B B] [A A A B B B] [A A A B B] [A A B B B]}).

In the present case, where the resulting alternatives are guaranteed
/not/ to be in either input policy, "intersection" seems stretched past
the breaking point.

I'm still not clear what use case justifies having to keep duplicates
around.  In all honesty that to me seems like a purely technical
requirement, and I'm not even sure what the technical grounds would be.

Ashok Malhotra wrote:
>
> Let us assume that duplicate alternatives have been removed from the
> normal form of both policies.
>
> Now, we have 2 sets of alternatives.  If we intersect these 2 sets we
> get as the result the alternatives that are common to both sets.
>  Isn’t this what we want?  So, I think intersection, explained as
> above is the correct term.
>
> All the best, Ashok
>
> ------------------------------------------------------------------------
>
> *From:* public-ws-policy-request@w3.org
> [mailto:public-ws-policy-request@w3.org] *On Behalf Of *David Hull
> *Sent:* Wednesday, May 16, 2007 8:31 PM
> *To:* Asir Vedamuthu
> *Cc:* Paul Cotton; public-ws-policy@w3.org
> *Subject:* Re: [Bug 4555] Should policy intersection be called policy
> intersection?
>
>  
>
> Asir Vedamuthu wrote:
>
>> In short, it seems misleading to call "pairwise combination (see 4553)
>> of compatible alternatives" "intersection", even though it does in
>> some cases act like intersection.
>>     
>  
> It is tempting to think of policy intersection as a set intersection but it is not (for all the reasons that you outlined below). This is why it is called as "Policy Intersection".
>   
>
> In my experience in trying to understand Policy Intersection, the fact
> that it was called "intersection" was a hindrance, not a help, in
> understanding what was going on.  It's not peanut butter either. 
> Calling it "Policy Peanut Butter"would distinguish it from "peanut
> butter" but would not aid in understanding (though it might still be
> an improvement).
>
> I would have found, say, "Policy Collation" more neutral and thus less
> misleading.
>
>  
> Regards,
>  
> Asir S Vedamuthu
> Microsoft Corporation
>  
>  
> -----Original Message-----
> From: public-ws-policy-request@w3.org <mailto:public-ws-policy-request@w3.org> [mailto:public-ws-policy-request@w3.org] On Behalf Of Paul Cotton
> Sent: Sunday, May 13, 2007 12:20 PM
> To: public-ws-policy@w3.org <mailto:public-ws-policy@w3.org>
> Cc: dmh@tibco.com <mailto:dmh@tibco.com>
> Subject: [Bug 4555] Should policy intersection be called policy intersection?
>  
>  
> -----Original Message-----
> From: public-ws-policy-qa-request@w3.org <mailto:public-ws-policy-qa-request@w3.org> [mailto:public-ws-policy-qa-request@w3.org] On Behalf Of bugzilla@wiggum.w3.org <mailto:bugzilla@wiggum.w3.org>
> Sent: May 11, 2007 12:02 PM
> To: public-ws-policy-qa@w3.org <mailto:public-ws-policy-qa@w3.org>
> Subject: [Bug 4555] Should policy intersection be called policy intersection?
>  
>  
> http://www.w3.org/Bugs/Public/show_bug.cgi?id=4555
>  
>            Summary: Should policy intersection be called policy
>                     intersection?
>            Product: WS-Policy
>            Version: CR
>           Platform: All
>         OS/Version: All
>             Status: NEW
>           Severity: normal
>           Priority: P2
>          Component: Framework
>         AssignedTo: fsasaki@w3.org <mailto:fsasaki@w3.org>
>         ReportedBy: dmh@tibco.com <mailto:dmh@tibco.com>
>          QAContact: public-ws-policy-qa@w3.org <mailto:public-ws-policy-qa@w3.org>
>  
>  
> The use of "intersection" to describe the operation approximated in section 4.5
> is problematic.
>  
> Intersection usually refers to set intersection of some sort (it might also
> refer to bag intersection, given that at least some collections in WS-P are
> bags).  Assuming that policies are sets (see 4552), there is some resemblance
> between set intersection and policy intersection, in that if it so happens that
> alternatives are compatible only when they're identical, the intersection of
> two policies will contain one item for each of the alternatives in the set
> intersection of the two policies.  If intersection of alternatives turns out to
> mean bag intersection (see 4553), then in this particular case policy
> intersection will be the set intersection of the two policies.
>  
> However, if these exact conditions don't hold, then the result is not at all
> the set intersection of the two polices.  In particular, two alternatives with
> the same assertions but different multiplicities will be compatible, and
> alternatives may be compatible even if their component assertions are not
> identical, if the assertions are of the same type (or are ignorable in the case
> of lax intersection).  In such cases the result may have more alternatives than
> either of the policies being intersected, which is counter-intuitive to say the
> least.
>  
> In short, it seems misleading to call "pairwise combination (see 4553) of
> compatible alternatives" "intersection", even though it does in some cases act
> like intersection.
>  
>  
>   
>
>  
>
Received on Wednesday, 23 May 2007 16:53:00 UTC

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