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Re: Caching data returned from POST, and conditional POST

From: Shel Kaphan <sjk@amazon.com>
Date: Sun, 31 Dec 1995 17:47:11 -0800
Message-Id: <199601010147.RAA04450@bert.amazon.com>
To: http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com, Brian Gaines <gaines@cpsc.ucalgary.ca>


Brian Gaines writes:
	...
 What Netscape sends is:-
	[ ... ]

 Since this is a POST with an "If-Modified-Since:" field I am calling it
 a conditional POST. If you interpret it as something else then I'd be
 interested to know your reasoning.

No, conditional POST is precisely what I'd call it.  I'm just
surprised to see it exists.

 As I noted previously, conditional POSTs make the same sense as conditional
 GETs so there is nothing wrong with what Nescape is doing. It does not
 conform with the specification but it is the spec that is wrong in making
 inessential differences between GETs and POSTs.

My main concern about this is that it that if such things propagate
then it needs to be clearly spelled out that the *action* at the
origin server is not modified by the existence of the "if-modified-since",
only the presence or absence of an entity in the response.   I suspect
there are other complications I am not thinking of right now, too.

 >Sorry, but most users do *not* equate the BACK button with "undo", and
 >in fact, most naive users don't know there's a difference between a
 >link that says "go back" and using the browser's BACK button, and to
 >the extent it is possible to preserve the lack of requirement for
 >users to know how these things work, I think it should be preserved.
 >

 Your sequence of statements seem conflicting.

??

 Naive users are totally
 unaware of the existence of "Undo" precisely because they just click
 on "Back" and things are naturally undone.

As long as that fits the model of what they're doing right then, they
won't notice...

 We have undertaken
 usability studies of the web and users do definitely use the "Back" button
 as an "undo" without any specific instructions to do so. It gives them a
 great sense of security to know that they can just back out of a transaction.
 As you say, they just jump back to a past state and they assume the world
 is no in that state.

Are your usability studies in the paper you cited earlier?  I'd like
to see them.  I can believe there are some situations where what you
say will work, but I can also give examples where it won't.  The usual
shopping basket example suffices.  If you have a search form followed
by a "put this in my shopping basket" form, and the user backs up to
the search form to select another item, and finds that the first item
is no longer in the shopping basket, I guarantee they will not find
that to be intuitive.
	...
 b.

 Dr Brian R Gaines               Knowledge Science Institute
				 University of Calgary
 gaines@cpsc.ucalgary.ca         Calgary, Alberta, Canada T2N 1N4
 403-220-5901  Fax:403-284-4707  http://ksi.cpsc.ucalgary.ca/KSI


Shel Kaphan
sjk@amazon.com
Received on Sunday, 31 December 1995 17:53:57 EST

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