Re: Auto-Download tags/function?

Tony Sanders (sanders@BSDI.COM)
Thu, 19 May 1994 15:03:37 -0500

"Daniel W. Connolly" writes:
> The way I understand it, the URI: header is a way for the server
> to tell the client "here's the name for the document I'm sending you.
> It's available in these formats, and that's it."
> I don't understand how that allows me to represent, in a document,
> a link to a specific format of a document.
First of all, you don't want people creating links to specific formats,
that defeats the whole point of format negotiation. Stored links should
be to the most varient form of the URI except in very special cases.

What proxies need to know is more about how format negotiation works so
they can short circut a request to a varient URI with something in the
cache but your proposal doesn't do anything to address that. Right now
a cacheing proxy must use some kind of heuristic and that should possibly
be addressed. I suppose the proxy would need some way to ask the
server about it's conversions. That could get real nasty though
(how good, how fast, from what to what, etc). Ugh!

If all you want is links to specific data sets URI: works like this.
Let's say you access and you get this back:
Last-Modified: Sunday, 08-May-94 20:48:20 GMT
Date: Thursday, 19-May-94 19:06:21 GMT
URI:; vary=content-type,version,language
URI:; vary=content-type,version,language
URI:; vary=language,version
URI:; vary=version
Content-Language: en_US
MIME-Version: 1.0
Content-Type: text/html
Then you know that (for as long
as it's valid) will return the exact same bits as you have in your hand
right now and you know that those bits are text/html in en_US.
The format of the URL in this scheme is total up to the server, it could
just as well be ``URI:''.

Please explain and give a specific protocol transaction where your scheme
of encoding the content-type in a standard way inside the HTTP URL is any
better than this.