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From Gianugo Rabellino <>
Subject Re: [RT]Cache/proxy friendly HTTP headers
Date Mon, 14 Jan 2002 22:43:50 GMT
Carsten Ziegeler wrote:

>>But first let's see if we all agree on this: caching and expires are a 
>>bit different. Caching is there to check if a resource *has changed* and 
>>act accordingly. Expires headers are there to *state* if and how a 
>>resource *will change* so in the end they might drive (override) the 
>>cache itself. See the difference? So we can say that, if an expires 
>>directive is present the cache should honor it: if it's not yet expired 
>>then the cache should avoid even checking the resources and send right 
>>away the final result, together with an appropriate Expires header. This 
>>way we have two speed improvements:


> Ok, yes, caching and expires a different things. You can set expires
> without caching anything. So a NonCachingPipeline can also set an expires
> date.
> The second thing you propose that - if a caching pipeline is used - the
> cache itself takes the expires date given in the sitemap to validate
> the cached content, should be very easy to implement. I guess that
> this would come to four lines java code. Sounds this easy enough? :)

If you know where those lines are to be placed definitely it does. ;) 
I'm a bit puzzled in finding exactly what is the correct way to extend 
the sitemap syntax in order to allow for the "expires" definition: I'll 
give it a deeper look in the next days.

This rises another intersting question though: if we are heading to 
different sitemap implementations (interpreted, compiled, scheme based) 
it might be tricky to get all versions in sync when a new semantic is 



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