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Re: About sniffing

From: <noah_mendelsohn@us.ibm.com>
Date: Mon, 22 Mar 2010 17:34:19 -0400
To: John Kemp <john@jkemp.net>
Cc: "www-tag@w3.org WG" <www-tag@w3.org>
Message-ID: <OF486A35CD.514E68B7-ON852576EE.00766672-852576EE.00768181@lotus.com>
> I apologize for only editing one of the two agendas - I hadn't realized 
that editing two files was necessary. 

No problem.  Glad I caught it though.  All set.

> It's a shame that we're using CVS instead of Subversion

That's a W3C sys team call.  I suspect that, at this point, they have some 
special-purpose hooks into CVS to drive things like mirroring, and I don't 
know what it would take for them to support Subversion.


Noah Mendelsohn 
IBM Corporation
One Rogers Street
Cambridge, MA 02142

John Kemp <john@jkemp.net>
03/22/2010 05:19 PM
        To:     noah_mendelsohn@us.ibm.com
        cc:     "www-tag@w3.org WG" <www-tag@w3.org>
        Subject:        Re: About sniffing

On Mar 22, 2010, at 3:22 PM, noah_mendelsohn@us.ibm.com wrote:

>> I'll update the agenda to list these and a link to this email
> BTW, note that there are two copies of the agenda [1,2], and it's 
> important that they both be edited when changes are made.  I haven't 
> unscrambled the CVS conflicts I'm seeing, but I see some hints that the 
> two copies got out of sync, perhaps due to your edits or others.

I updated my repository this morning, and made changes to that copy 
immediately. When I committed, I wasn't warned about having an old 
version, so I would suggest that my edits were made on the latest 
committed copy. 

>  I 
> believe that I have managed to reconstruct in both copies the edits you 
> made, but there is some chance I didn't succeed, and in the future I 
> commit that changes made in only one copy won't later be lost.  FYI, my 
> usual procedure is usually to check out one copy, edit it, check it in, 
> then copy that blindly over a checked out version of the other copy. So, 

> if you only edit one copy, you risk getting your edits backleveled, and 
> there's a certainty that readers of the other copy won't see them.

It's a shame that we're using CVS instead of Subversion, which supports 
symbolic links (ie. you'd only need to change one file and link to it from 
the other place).

I apologize for only editing one of the two agendas - I hadn't realized 
that editing two files was necessary. 


- johnk

> Noah
> [1] http://www.w3.org/2001/tag/2010/03/24-agenda.html
> [2] http://www.w3.org/2001/tag/tag-weekly
> --------------------------------------
> Noah Mendelsohn 
> IBM Corporation
> One Rogers Street
> Cambridge, MA 02142
> 1-617-693-4036
> --------------------------------------
> John Kemp <john@jkemp.net>
> Sent by: www-tag-request@w3.org
> 03/22/2010 11:17 AM
>        To:     "www-tag@w3.org WG" <www-tag@w3.org>
>        cc:     (bcc: Noah Mendelsohn/Cambridge/IBM)
>        Subject:        About sniffing
> Hello,
> Below, I have written some suggested goals for our f2f discussion (I'll 
> update the agenda to list these and a link to this email), and some 
> from my recent re-reading of the Authoritative Metadata finding - 
> http://www.w3.org/2001/tag/doc/mime-respect. I realize I can't make this 

> "required reading" at this late stage, but I would suggest that people 
> least read my notes below, but preferably read the Authoritative 
> finding itself to get a good background for this issue. 
> I believe this email to be related to ACTION-399.
> Regards,
> - johnk
> Sniffing discussion goals
> -------------------------------
> * Discuss what (if anything) can be done by the TAG to improve the 
> situation of content-type mis-labeling errors and reporting.
> * Discuss the requirements for a content-sniffing algorithm given the 
> constraints discussed in Authoritative Metadata, and in relation to the 
> content-sniffing draft proposed in 
> http://tools.ietf.org/html/draft-abarth-mime-sniff-04 
> * Establish any updates to Authoritative Metadata and Self-describing 
> findings based on these discussions.
> * Discuss other instances of sniffing, as noted by Larry in email to 
> "I think this general rule should apply to MIME 
> types, HTML versions, charset labels and language
> tags (four kinds of 'sniffing' currently covered
> by the HTML document.)"
> Reading Authoritative Metadata (AM)
> -----------------------------------------------
> Arguments *against* the summary of key points from AM finding:
> i) Why should metadata in an "encapsulating container" be authoritative? 

> What happens when the container is separated from the contained entity? 
> What about publishing chains where mis-labelling occurs?
> ii) Inconsistency between representation data and metadata is an error 
> which MUST not be silently ignored. To make the situation better, we 
> to provide guidance that supports such correction - browser plugins that 

> report inconsistencies to the origin server owner? Content-management 
> system plugins that sniff uploaded content and report errors?
> iii) Why must an agent not override content-type without user consent? 
> Source view vs content view - when source is plain text and content is 
> interpretation of plain text it must be possible to display both...
> "For Web architecture, a design choice has been made that metadata 
> received in an encapsulating container MUST be considered authoritative" 
> why!? Section 3 attempts to describe why....
> Why (summarized):
> i) Make media types descriptive of intended interpretation, not just an 
> indication of format.
> This requires that media types are properly descriptive and registered 
> accurately. This also doesn't deal with the mis-labeling problem (ie 
> type is there but doesn't accurately describe the proper interpretation. 

> In order to make this true, servers should sniff and detect mislabeled 
> content received from clients too. 
> ii) If container metadata is not used, and sniffing is required, only 
> representation of the content is possible - thus container metadata MUST 

> be possible. 
> Agree with this
> iii) Using the container metadata model allows easier dispatch to 
> "handlers/plugins" without recourse to inspecting the message body
> Agree with this
> What to do when no metadata is supplied:
> * If Content-type is EMPTY, UA MAY sniff
> * If Content-type is application/octet-stream, UA should ask the user 
> (this is not said in AM, but appears common convention - AM says: 
> managers (webmasters) SHOULD NOT specify an arbitrary Internet media 
> (e.g., "text/plain" or "application/octet-stream") when the media type 
> unknown.")
> Servers and clients should be more circumspect about labeling content - 
> and say "I don't know" (empty Content-type) more often. 
> From AM: "Instead of specifying a default for metadata, it is better for 

> representations to be sent without that metadata. That allows the 
> recipient to guess the metadata instead of being forced to either accept 

> incorrect metadata or be tempted to violate Web architecture by ignoring 

> it."
> and...
> "It is better to send no media type if the resource owner has failed to 
> define one for a given representation."
> Conclusion: Authoritative Metadata finding accurately describes the 
> and does its best to give good guidance.
Received on Monday, 22 March 2010 21:34:53 UTC

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