I'm engaged in trying to convince a large well-known organization to take Atom seriously (I think I'm winning) and we had this email exchange, which I thought might be useful as a refresher for those who have blissfully forgotten the great updated/modified debate.
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I think the biggest concern right now is that that the LastUpdated date can be left unchanged even when the post IS changed (e.g. spelling corrections)
What you want is reasonable to want but unfortunately no syndication format can give it to you. Here is the current language:
The "atom:updated" element is a Date construct indicating the
most recent instant in time when an entry or feed was modified
in a way the publisher considers significant.There was a proposal for an "atom:modified" date that was to be updated every time any change no matter how tiny was made but it was shouted down. There were many arguments against, but here are three that I couldn't think of an answer to:
1. The datestamp is inserted by the provider. Thus it could be a lie; this is the Internet, remember. You, the consumer, either trust the publisher or you don't. If you don't, you will ignore the datestamp and check the content. If you do, you will believe the datestamp. Thus, "modified" buys you nothing.
2. There's endless room for argument as to what constitutes an update: change in the stylesheet for background colors, change from a unicode combined char to single + combining diacritic, change in paragraph 27 of an article that doesn't show up in a summaries-only feed, change from UTF-8 to UTF-16 encoding, there were more examples too, some of them scary-subtle.
3. Several publishers on the list asserted that they needed the right to make trivial spelling-correction-level changes without having a zillion literal-minded feed-reading clients re-fetch the material, and that they would simply refuse to update an atom:modified date if they didn't feel like it.
Objectively, the upstream information provider controls the datestamps. If you can think of a way to write a syndication format that will function across the Internet and reliably force providers to provide accurate "modified" indicators, there are a lot of people who would like to hear about it.
