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

From: <bugzilla@wiggum.w3.org>
Date: Fri, 11 May 2007 16:01:44 +0000
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To: public-ws-policy-qa@w3.org
Message-Id: <E1HmXYu-0007xF-6N@wiggum.w3.org>

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
        ReportedBy: dmh@tibco.com
         QAContact: 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 Friday, 11 May 2007 16:01:46 GMT

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