Re: I want have "Last-modified:" in HTTP/1.0 headers

Steve Putz (
Fri, 12 Nov 1993 13:39:16 PST

Marc VanHeyningen <> wrote:
> Short of having every example of a gateway coded in, how could a cache
> server possibly tell the difference?
> Rhetorical question. Answer: The Expires: header. It's the
> responsibility of the server to make available an indication of how
> long that information will remain "current".

Is that what we want "Exipres" to mean? In both my examples, the
information from the gateways does not expire or become obsolete.
Rather I was suggesting that the likelyhood of a cache hit can be small
because the virtual information space is so large.

For example, users will rarely click on the exact same latitude and
longitude in the map viewer, and the cost of caching the resulting GIF
image is high. On the other hand if someone widely publishes a URL for
a particular map, caching makes sense.

My point is that choosing caching strategies becomes more difficult as
the information space gets richer. The Expires: header does not really
solve the problem.

Steve Putz
Xerox PARC