On Tue, 14 Nov 1995, Jeffrey Mogul wrote: > If you recall, I suggested that an object without an explicit Expires: > header attached must always be validated by a proxy. There are three > cases: > Expires: missing > validation required on every fetch from any cache > Expires: "never" > validation never required (immutable documents) > Expires: <some timestamp> > validation not required until <timestamp>, but > always required after that. Okay, this would seem to solve the problem conditions I can think of. > That said, I think what we need for doing conditional requests is a > general grammar to which we can apply file attributes. Something like [my proposal for Send-If, which I was informed was proposed at one point for HTTP as "Unless:", and will hopefully be in 1.1 - cool] > But this implies that the clients and servers share a deep understanding > of the attributes of the objects. What about objects that don't have > "modification times"? What other attributes could be both useful and > generally supported? I'm as much of a fan of file attributes as anyone > (after all, I did my PhD dissertation on the topic), but I don't think > we should be pushing HTTP in that direction. HTTP is not a file > access protocol. My mistake for calling them file attributes rather than object attributes - while you might refrain from calling it a "file access protocol", I think we could certainly agree to call it an "object request protocol". To some extent, "Send Unless" and conditional GETs are just an optimization over doing a HEAD request on an object before fetching it, so i'm not going to proclaim that the WWW will fall apart if it's not implemented. > And if someone does come up with another use for attributes, are these > really the right thing to use for cache validation? I think not. I will defer to the cache validation experts. Of which there don't seem to be many :) Brian --=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-- brian@organic.com brian@hyperreal.com http://www.[hyperreal,organic].com/Received on Tuesday, 14 November 1995 14:16:24 UTC
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