Re: [apps-discuss] Fwd: New Version Notification for draft-shelby-exi-registration-01.txt (Henry S. Thompson) Wed, 11 April 2012 15:15 UTC

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To: Carsten Bormann <>
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From: (Henry S. Thompson)
Date: Wed, 11 Apr 2012 16:15:12 +0100
In-Reply-To: <> (Carsten Bormann's message of "Wed, 11 Apr 2012 14:04:05 +0200")
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Subject: Re: [apps-discuss] Fwd: New Version Notification for draft-shelby-exi-registration-01.txt
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Carsten Bormann writes:

> EXI requires out of band information to use the "Schema-Informed"
> mode.  In the Internet, This would normally be provided in an
> Internet media-type definition.  The media-type definition may also
> want to constrain the allowable values for the numerous options EXI
> provides, allowing for constrained implementations of EXI.

Your conclusion (use media type) doesn't follow.  Consider the analogy
of Content-Encoding: gzip -- suppose gzip provided improved
performance based on the decade in which the encoded document was
written, since natural language priors slowly shift over time.  Now
decoding requires OOB information about document creation date.  How shall
we provide it.  I know -- we'll define media types
application/...+gzip for every decade of interest!  I hope it's
obvious that would be a mistake. . .

If decoding requires some parameters, surely the right thing to do is
to transmit them in the obvious place, i.e. in the response message

Either use the Content-Encoding (and Accept-Encoding) header itself,
by registering a new Content-Coding value [1] (foo+exi), or (better)
ask the W3C EXI WG to publish a Note defining an extension-header for
specifying or requesting a schemaID (and more generally, perhaps,
other properties specifiable in the EXI Options docuemtns).

Not only would the second option fit the architecture better, it would
remove the necessity for publishing a new RFC every time you update
the relevant schema!


       Henry S. Thompson, School of Informatics, University of Edinburgh
      10 Crichton Street, Edinburgh EH8 9AB, SCOTLAND -- (44) 131 650-4440
                Fax: (44) 131 650-4587, e-mail:
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