Point out the potential for denial of service by duplicating others' atom:id values.
We want atom:id to be univerally unique to a particular entry resource.
However, depending on such uniqueness could lead to denial of service attacks where the attacker publishes an entry with an atom:id value used by someone else.
Restricting the uniqueness scope of atom:id entirely to a single feed would make it much less valuable, since entries are often copied form feed to feed, and sometimes simultaneously published in multiple feeds.
Only requiring entries with the same atom:id to be considered the same if coming from the same feed, but allowing the consuming application to exercize judgement with respect to entries originating in different feeds is a much better match with reality.
Still, pointing out the potential for DOS attacks in the Security Considerations section may be preferable to loosening the scope of atom:id uniqueness elsewhere in the spec in either of the ways describe by the preceding bullet points.
Add the following to format-08:
8.5 Denial of Service Attacks
Atom Processors should be aware of the potential for denial of service attacks where the attacker publishes an atom:entry with the atom:id value of an entry from another feed, and perhaps with a falsified atom:source element duplicating the atom:id of the other feed. Atom Processors which, for example, suppress display of duplicate entries by displaying only one entry with a particular atom:id value or combination of atom:id and atom:updated values, might also take steps to determine whether the entries originated from the same publisher before considering them to be duplicates.
An alternative to PaceDuplicateIdsEntryOrigin