RE: Collections: Sets, bags or something else?

David Hull wrote:
> In that case, define policies as sets of alternatives, as there
appears to be no reason to deviate from that well-established
abstraction.

I agree...cheers,
BobN

________________________________

	From: public-ws-policy-request@w3.org
[mailto:public-ws-policy-request@w3.org] On Behalf Of David Hull
	Sent: Wednesday, May 02, 2007 12:07 PM
	To: Asir Vedamuthu
	Cc: public-ws-policy@w3.org
	Subject: Re: Collections: Sets, bags or something else?
	
	
	Asir Vedamuthu wrote: 

		> that "collection" here means "unordered collection
with 

		>duplicates allowed", informally known as a "bag".
		>Is this the intended meaning?

		

		Yes

		

		>If the intended meaning is to allow duplicates, is
there 

		>any special meaning to the same alternative appearing
more than 

		>once in a policy

		

		No

	In that case, define policies as sets of alternatives, as there
appears to be no reason to deviate from that well-established
abstraction.
	
	In general, it seems risky to use off-the-beaten-path concepts
like bags unless there is some compelling reason to do so.
Intersection of alternatives is a case in point.  If alternatives were
sets, not bags, the definition of intersection could (AFAICT) say "set
union" or "set intersection"(whichever was appropriate) and there would
be no room for misunderstanding.  As it is, you're effectively defining
"bag intersection" or "bag union", or perhaps something else, on the
fly.
	
	In the case of policies as sets of alternatives, it would be
clear that order and multiplicity don't matter, only what is or isn't
in the set -- in this case, what alternatives are or are not available.
	

		

		

		We hope this helps.

		

		Regards,

		

		Asir S Vedamuthu

		Microsoft Corporation

		

		

		From: public-ws-policy-request@w3.org
[mailto:public-ws-policy-request@w3.org] On Behalf Of David Hull
		Sent: Monday, April 30, 2007 10:24 PM
		To: public-ws-policy@w3.org
		Subject: Collections: Sets, bags or something else?

		

		A follow-up to my previous:
		
		The spec appears to carefully use "collection" and not
"set".  This, together with the absence of expression equivalence rules
like a+a=a and a*a=a and the note that assertions of the same type may
occur in an alternative, suggest that "collection" here means
"unordered collection with duplicates allowed", informally known as a
"bag".
		
		Is this the intended meaning?  It's not unheard of to
use "collection" to mean "set" (i.e., duplicates are not considered).
If the intended meaning is to allow duplicates, is there any special
meaning to the same alternative appearing more than once in a policy
(as opposed to the same assertion (type?) appearing more than once in
an alternative, which behavior is out of scope).