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Re: Meaning of Last-Modified/I-M-S (was Re: Last gasp terminology issue)

From: Larry Masinter <masinter@parc.xerox.com>
Date: Tue, 4 Jun 1996 16:21:33 PDT
To: john@math.nwu.edu
Cc: mogul@pa.dec.com, fielding@liege.ICS.UCI.EDU, http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
Message-Id: <96Jun4.162137pdt.2733@golden.parc.xerox.com>
The last-modified date of a response should be the latest time at
which the given response became a valid response for the given
request (or any variations of the request as specified by the VARY
header.)

For web servers that are based on file systems, the "last-modified"
time corresponds to the last time the file was modified, both for the
case where there is a single file and when there are a fixed number of
files and the appropriate file is chosen according to request headers.

However, if you add a new file to the set, the 'last-modified' date of
other members of the set would also change, so the CERN and Apache
heuristic of using the maximum over all of the variants is a good
conservative heuristic.

For those web servers that do dynamic document construction or
server-side includes based on content negotiation, other kinds of
internal behavior might be more appropriate; this is why the protocol
should not require any particular implementation.

Larry
Received on Tuesday, 4 June 1996 16:23:43 EDT

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