Re: Finishing(!) the XML-tagging discussion
ned.freed@INNOSOFT.COM Tue, 21 March 2000 16:41 UTC
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From: ned.freed@INNOSOFT.COM
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Date: Tue, 21 Mar 2000 08:03:29 -0800
Subject: Re: Finishing(!) the XML-tagging discussion
In-reply-to: "Your message dated Tue, 21 Mar 2000 08:26:34 -0500" <200003211326.IAA19007@astro.cs.utk.edu>
To: Keith Moore <moore@cs.utk.edu>
Cc: Graham Klyne <GK@dial.pipex.com>, Keith Moore <moore@cs.utk.edu>, ietf-xml-mime@imc.org
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(Apologies in advance for the syntax of my examples here. I'm not bothering to check them carefully.) > my position is that requiring a separate label to facilitate > content negotiation makes it entirely too likely that the > separate label will be incorrect or omitted. so any proposal > for an xml frob that says "don't use this frob for content-negotiation" > is a non-starter - it's headed 180 degrees in the wrong direction. Keith, with all due respect, this strikes me as a fine academically pure view, but unfortunately one that's entirely divorced from reality. The reality is that feature expressions and their associated tags are being used in at least four different ways: (1) As a standalone negotiation mechanism. (2) As an adjunct to an existing negotiation mechanism. (3) As a standalone means of labelling objects. (4) As an adjunct to an existing object labelling mechanism. These multiple different uses make it inevitable that tags will be registered that result in silly states. Consider, for example, (1) and (2). (1) as manifested in Internet FAX makes it necessary to register things like media types and charsets as feature tags. But (2) as manifested in HTTP leads to the possibility of: accept-charset: UTF-8 accept-features: (charset=ISO-2022-JP) Or consider (3) and (4). (3) again requires registration of things like media types. But (4) in the case of email makes it possible to say: content-features: (media-type="text/plain") content-type: application/octet-stream Now, the only ways I can think of to address this problem are: (a) Prohibit the registration of tags that duplicate other labels. Problem is, this breaks (1) and (3) completely, and also breaks (2) and (4) in cases where some labels from other contexts aren't available. So this dog doesn't hunt. (b) Prohibit the use of tags in a given context that duplicate labels used in that context. Problem is that such a rule is quite difficult to write given that the existing label set is a moving target in many contexts, and effectively unenforceable in any case. So this dog doesn't hunt either. (c) Prohibit the use of tags whose values conflict with the labels in a given context. But this amounts to sayin, "Don't produce stuff with silly states"; it doesn't provide the guarantee you're demanding. (d) Have different sorts of feature expressions for the different cases. But this multiplies the number of mechanisms to a ridiculous degree. Moreover, given the complexity of feature expressions it actually is possible to have silly states within a single expression: accept-features: (&((charset=UTF-8),(charset=ISO-2022-JP))) accept-features: (&((language=ger),(language=fre))) And ironically, determining that an arbitrary feature expression actually describes a silly state turns out to be NP-hard! (It's obviously equivalent to the classic satisfiability problem.) The bottom line here is that silly states abound in the world of content negotiation. That's the nature of the beast, and there's nothing you can do to change it. You are tilting at windmills here. This is why I've always considered the criteria for viable content negotiation labelling to be totally separate from the straightforward labelling we've been talking about here. Trying to combine the two inevitably creates requirements that are, so to speak, unsatisfiale. Now, let's return for a moment to the issue at hand (please note I didn't use XML once in any of the above examples). I've said previously that your proposal of a content-type parameter leads directly and inevitably to a new feature tag being needed, so if new feature tags are unacceptable to you your own proposal has to be unacceptable as well. It occurs to me that some of the readers of this thread may not understand why this is so. The reason is simple: The defined mechanism for putting content-type information in feature expressions (draft-ietf-conneg-content-features-02.txt) provides a means of checking media types in feature expressions but no means of checking that a given parameter is present on an arbitrary media type. And the current doctrine is that rather than developing a mechanism for checking arbitray media type parameters those parameters important enough to check will receive their own tag. See, for example, draft-hoffman-char-lang-media-02.txt, where one such tag is proposed. Amusingly enough, I sent a note to the IESG arguing that the omission of a facility to check MIME parameters in feature expressions was an oversight that should be corrected. But I was alone in believing this, so it didn't happen. (You were, as I recall, supportive of the document as-is and silent on this particular point.) Ned
- Re: Finishing the XML-tagging discussion Tim Bray
- Re: Finishing(!) the XML-tagging discussion ned.freed
- Re: Finishing(!) the XML-tagging discussion Graham Klyne
- Re: Finishing the XML-tagging discussion Simon St.Laurent
- Re: Finishing(!) the XML-tagging discussion Martin J. Duerst
- Re: Finishing the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion Tim Bray
- Re: Finishing the XML-tagging discussion John Cowan
- Re: Finishing the XML-tagging discussion John Cowan
- Re: Finishing the XML-tagging discussion Tim Bray
- Re: Finishing the XML-tagging discussion John Cowan
- Re: Finishing the XML-tagging discussion Tim Bray
- Re: Finishing(!) the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion Graham Klyne
- Re: Finishing the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion John Cowan
- Re: Finishing the XML-tagging discussion ned.freed
- Re: Finishing(!) the XML-tagging discussion Keith Moore
- Re: Finishing the XML-tagging discussion Keith Moore
- Re: Finishing(!) the XML-tagging discussion Graham Klyne
- Re: Finishing the XML-tagging discussion Graham Klyne
- Re: Finishing the XML-tagging discussion Graham Klyne
- Re: Finishing the XML-tagging discussion Valdis.Kletnieks
- Re: Finishing the XML-tagging discussion Valdis.Kletnieks
- Re: Finishing the XML-tagging discussion Martin J. Duerst
- Re: Finishing the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion Keith Moore
- Re: Finishing the XML-tagging discussion Martin J. Duerst
- Re: Finishing the XML-tagging discussion Simon St.Laurent
- Re: Finishing the XML-tagging discussion Keith Moore
- Re: Finishing the XML-tagging discussion Martin J. Duerst
- Re: Finishing the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion ned.freed
- RE: Finishing the XML-tagging discussion Dan Kohn
- Re: Finishing the XML-tagging discussion Simon St.Laurent
- Re: Finishing the XML-tagging discussion Keith Moore
- Re: Finishing the XML-tagging discussion Keith Moore
- Re: Finishing the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion Simon St.Laurent
- Re: Finishing the XML-tagging discussion Keith Moore
- Re: Finishing the XML-tagging discussion Keith Moore
- Re: Finishing the XML-tagging discussion Keith Moore
- Re: Finishing the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion Simon St.Laurent
- Re: Finishing the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion Keith Moore
- Re: Finishing the XML-tagging discussion Keith Moore
- Re: Finishing the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion Simon St.Laurent
- Re: Finishing the XML-tagging discussion Keith Moore
- Re: Finishing the XML-tagging discussion Keith Moore
- Re: Finishing the XML-tagging discussion Simon St.Laurent
- Re: Finishing the XML-tagging discussion Keith Moore
- Re: Finishing the XML-tagging discussion Keith Moore
- Re: Finishing the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion Tim Bray
- RE: Finishing the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion Marshall Rose
- Re: Finishing the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion Simon St.Laurent
- Re: Finishing the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion ned.freed
- RE: Finishing the XML-tagging discussion Miles Sabin
- Re: Finishing the XML-tagging discussion Marshall Rose
- Re: Finishing the XML-tagging discussion Keith Moore
- Re: Finishing the XML-tagging discussion Simon St.Laurent
- Re: Finishing the XML-tagging discussion Keith Moore
- Re: Finishing the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion Keith Moore
- Re: Finishing the XML-tagging discussion Chris Lilley
- Re: Finishing the XML-tagging discussion Graham Klyne
- Re: Finishing the XML-tagging discussion Simon St.Laurent
- Re: Finishing the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion Elliotte Rusty Harold
- Re: Finishing the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion Simon St.Laurent
- Re: Finishing the XML-tagging discussion Simon St.Laurent
- Re: Finishing the XML-tagging discussion by way of "Simon St.Laurent" <simonstl@simonstl.com>
- Re: Finishing the XML-tagging discussion Simon St.Laurent
- Re: Finishing the XML-tagging discussion Simon St.Laurent
- Re: Finishing the XML-tagging discussion Simon St.Laurent
- Re: Finishing the XML-tagging discussion Paul Hoffman / IMC
- Re: Finishing the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion Simon St.Laurent
- Re: Finishing the XML-tagging discussion Paul Hoffman / IMC
- Re: MIME types and content negotiation ned.freed
- Re: MIME types and content negotiation Simon St.Laurent
- Re: MIME types and content negotiation Graham Klyne
- Re: MIME types and content negotiation Simon St.Laurent
- Re: MIME types and content negotiation Graham Klyne
- Re: MIME types and content negotiation Graham Klyne
- Re: MIME types and content negotiation Keith Moore
- Re: MIME types and content negotiation Chris Lilley
- Re: MIME types and content negotiation Simon St.Laurent
- Re: MIME types and content negotiation Chris Lilley
- MIME types and content negotiation Simon St.Laurent
- Re: Finishing the XML-tagging discussion ned.freed
- Re: Finishing the XML-tagging discussion Simon St.Laurent
- Re: Finishing the XML-tagging discussion Harald Tveit Alvestrand
- Re: Finishing the XML-tagging discussion Tim Bray
- Re: Finishing the XML-tagging discussion Dan Crevier
- Finishing the XML-tagging discussion Paul Hoffman / IMC