State the atom:entries from the same feed with the same ID are the same entry, whether simulateously in the feed document or not.
Retracted by the author -- see PaceAtomIdDos instead
The accepted language for allowing duplicate IDs in a feed document speaks only multiple atom:entry elements with the same atom:id describing the same entry if they exist in the same document--of course, we intend for them to describe the same entry whether they're simultaneously in the feed document or not
The accepted language does not speak of the origin feed of the entries. Ideally, an atom:id should be univerally unique to one entry resource, and we rightly require publishers to mint them with that goal. However, in reality, malicious or undereducted publishers might duplicate the IDs of others. Therefore, it is proposed to modify the specification to state that the atom:entry elements describe the same entry (resource) if they originate in the same feed.
Aggregators wishing to protect against DOS attacks are not unlikely to perform some sort of safety checks to detect malicious atom:id duplication, regardless of whether the specification "authorizes" them to or not.
1. Remove this bullet point from 4.1.1:
atom:feed elements MUST NOT contain atom:entry elements with identical atom:id values.
2. Add the following paragraph, either to atom:entry or atom:feed, at the editors' discretion (instead of the first sentence proposed by PaceAllowDuplicateIDs, if accepted):
If multiple atom:entry elements originating in the same Atom feed have the same atom:id value, whether they exist simultaneously in one document or in different instances of the feed document, they describe the same entry.
Aggregators wishing to both perform duplicate detection and protect against DOS attacks will be justified by the specification in applying their judgement regarding whether entries with the same atom:id come from the same source or not.
Because we are unlikely to agree on a method for determining whether the atom:entry elements originate in the same feed or not, no particular method will be specified.
The proposed language does not preclude the possibility of aggregators applying their own judgement regarding whether two atom:entry elements with the same atom:id which originate in different feeds might describe the same entry resource, which they might if someone posts the same to entry to, for example, a category feed and a feed of all their categories, and doesn't present one as having been aggregated from the other by including an atom:source element.