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TAG review of EXI Best Practices

From: Henry S. Thompson <ht@inf.ed.ac.uk>
Date: Thu, 02 Oct 2008 14:43:08 +0100
To: public-exi@w3.org
Cc: www-tag@w3.org
Message-ID: <f5babdnf6z7.fsf@hildegard.inf.ed.ac.uk>

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On behalf of the TAG, we welcome the expression of the outcome of the
discussions at TPAC last year in this document [1].

Presuming this now 10-month-old draft continues to represent the WG's
position on the matter, we endorse the commitment to the 'Content
Encoding' route as the least-bad alternative available.  We would
encourage you, however, to devote a bit more space to explaining the
details of what this amounts to, in particular the way in which EXI as
specified cannot literally take the place of a Content Encoding:

 1) It doesn't map text to text;

 2) Even if a version of it were specified that did, it is not
    universal, that is, it _only_ maps XML to XML.

Compare this to for example gzip: gzip maps text to encoded text, and
back again, whereas EXI as spec'ed maps infosets to encoded text and
back again, so a message which says "Content-Encoding: gzip;
Content-Type: application/svg+xml" can be understood as saying "Unzip
this byte-stream and you'll get a message body to which normal
application/svg+xml processing can be applied", whereas a message
which says "Content-Encoding: x-gzip; Content-Type:
application/svg+xml" cannot be interpreted as saying "EXI-decode this
byte-stream, and you'll get a message to which normal
application/svg+xml processing can be applied", because the result of
the EXI decoding algorithm is not a message body, it's an Infoset.
And of course you can gzip anything, whereas you can only EXI-encode
XML.

ht, on behalf of the TAG [2]

[1] http://www.w3.org/TR/2007/WD-exi-best-practices-20071219/
[2] http://www.w3.org/2001/tag/group/track/actions/180
- -- 
       Henry S. Thompson, School of Informatics, University of Edinburgh
                         Half-time member of W3C Team
      10 Crichton Street, Edinburgh EH8 9AB, SCOTLAND -- (44) 131 650-4440
                Fax: (44) 131 651-1426, e-mail: ht@inf.ed.ac.uk
                       URL: http://www.ltg.ed.ac.uk/~ht/
[mail really from me _always_ has this .sig -- mail without it is forged spam]
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Received on Thursday, 2 October 2008 13:43:44 GMT

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