--On May 5, 2005 8:15:10 AM +0100 Andy Henderson <[EMAIL PROTECTED]> wrote: > > here is no RSS2 feature I can see that allows feed providers to tell > aggregators the minimum refresh period. There's the ttl tag. That was, I > believe, introduced for a different purpose and determines the Maximum time > a feed should be cached in a certain situation.
We need both a ttl (max-age) and expires. One or the other is appropriate for different publishing needs. We also need to specify what you do with those values, or you end up with a mess, like the RSS2 ttl meaning reversing over an undocumented value (Yikes!). > What has yet to be tried is a specific tag in the core feed standard that > promotes and determines good behaviour for aggregators refreshing their > feeds. Even if it were to prove only a limited benefit, it would still be a > benefit. It has been tried several ways, originally in robots.txt extensions and also in RSS. It doesn't work. The model is not rich enough for publishers or for spiders/aggregators. Max-age/expires is already designed and proven. By page count, 20% of the HTTP 1.1 spec is about caching. If we want to write a new caching/scheduling approach, we can expect it to be a 20 page spec, plus an additional 10 pages on how to work with the HTTP model. See the Notes section here for details on when to use max-age or expires, and on the problems with calendar-based schemes. <http://www.intertwingly.net/wiki/pie/PaceCaching> wunder -- Walter Underwood Principal Architect, Verity
