>>>we're designing a feed format here. When this feed is served through HTTP, (re-)using the caching features of HTTP will ensure that any standard HTTP client will take advantage of it. For instance, if you use an HTTP client component that maintains it's own cache, it will automatically do the right thing. Also, when you're accessing the feed through an HTTP proxy, you will get copies from the proxy's cache when available.<<<
Understood. My issue is that creating the headers is outside the capability of many (most?) feed providers. >>>I just checked and Apache allows you to set the "Expires" header through "mod_expires" (<http://httpd.apache.org/docs-2.0/mod/mod_expires.html>). <<< I'm sure you're right, but it would mean little to most feed providers (including me). >>>Lotus Domino seems to do it though a thing called "Web Site Rule" (<http://www-128.ibm.com/developerworks/lotus/library/dwa-clientperf/>). <<< DWA is a sub-feature of the mail client so not helpful, I'm afraid. Thanks for looking into it, though. >>>I'm sure you can do it with other packages as well.<<< If it was available at the blogging package level, I'm sure people that use those packages would use the feature. The fact few feeds seem to use the Expires header, and those that do use it to immediately expire, seems to indicate an issue (proxy caching?). >>>On the other hand, of the feeds you checked, how many did actually implement the corresponding RSS feature (<http://blogs.law.harvard.edu/tech/rss#ltttlgtSubelementOfLtchannelgt>)?<<< Out of 33 RSS.9/2 feeds, 16 have ttl tags. Syndic8 reports that 16,840 RSS feeds use it. It says that's 7% of the total. The actual percentage is better than that because I believe ttl is RSS2 only; it's certainly not RSS1. That's pretty high considering that ttl is flawed because it was not originally designed to communicate minimum refresh intervals. >>>If you can demonstrate that lots of feeds use thos feature, and that aggregators indeed pay attention to it, you may be able to convince the WG that Atom needs this to achive feature parity.<<< I've no way to demonstrate aggregator use except my own - even though I support a tiny community I do observe and enforce the ttl tag. I'm sure that if there were a clearly-defined tag supported by Mark's implementation document, usage would significantly improve over RSS2 ttl levels. As for convincing the WG, I would simply point out that a mechanism widely available to, and understood by, feed providers and aggregators cannot do harm and has the potential to do a great deal of good. It seems to me to be a useful opportunity to demonstrate a clear improvement over both RSS1 and RSS2. Andy
