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David Hull started this conversation by noting that where the Framework spec uses the word "collection", it really means "bag" as there is no order and duplicates are allowed. See http://lists.w3.org/Archives/Public/public-ws-policy/2007May/0001.html I replied, supporting this suggestion and noting that 'collection' is used in 3 contexts in the Framework spec: a policy is a collection of alternatives, am alternative is a collection of assertions and a policy scope is a collection of policy subjects. http://lists.w3.org/Archives/Public/public-ws-policy/2007May/0042.html Fabian responded saying that implementations could do what they wanted; specifically they could eliminate duplicates http://lists.w3.org/Archives/Public/public-ws-policy/2007May/0045.html Asir responded that the word 'bag' was too technical and suggested that we add the sentence "The items in a collection in this specification are unordered and may contain duplicates." See http://lists.w3.org/Archives/Public/public-ws-policy/2007May/0062.html
My understanding from the list discussion is that policies are *sets* of alternatives, not bags, in that it does not matter how many times an alternative appears, so long as it appears. If so, then the blanket statement that "collection" means "unordered collection with multiple occurrences allowed" is inappropriate. If policies are allowed to contain the same alternative multiple times, then someone has to say what the differences is between, e.g., an alternative occurring once and the same alternative occurring twice. Conversely, if there is no difference, then say so explicitly. That is, instead of saying "A policy is a collection (unordered, multiples allowed) of alternatives where multiplicity doesn't matter", say directly that "A policy is a set of alternatives".
<cferris> RESOLUTION: issue 4552 closed with text in http://lists.w3.org/Archives/Public/public-ws-policy/2007May/0062.html placed in Terminology section and referenced (linked) from uses of the term as deemed appropriate by editors
Reference - http://www.w3.org/2007/05/23-ws-policy-minutes.html#item08