Re: MPEG asks for MIME review for the MPEG21 file format

Chris Lilley <> Mon, 21 May 2007 15:26 UTC

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Date: Mon, 21 May 2007 17:26:03 +0200
From: Chris Lilley <>
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To: Graham Klyne <>
Cc: Dave Singer <>, Martin Duerst <>, Anne van Kesteren <>, Larry Masinter <>, <>, <>, "'Christian Timmerer (ITEC)'" <>, <>, <>
Subject: Re: MPEG asks for MIME review for the MPEG21 file format
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On Monday, May 21, 2007, 11:13:58 AM, Graham wrote:

GK> Chris Lilley wrote:
>> On Friday, May 18, 2007, 5:27:52 PM, Dave wrote:

>> (I'm snipping the parts already covered by Martin)

>> DS> Is a ZIP compressed XML file servable under a +xml MIME type? 
>> DS> "encoding='zipped Shift_JIS'"?

>> I suspect you mean gzip, which is a compression method; zip is an archive format (often compressed internally).

>> If you started with foo.xml in Shift_JIS, the encoding declaration would say just that. If you then make foo.xml.gz the encoding declaration (when decompressed) says exactly the same thing. The fact that is been gzipped is conveyed out of band, in the http headers:

>> Content-Encoding: gzip

>> There is scope for confusion, since XML uses 'encoding' for 'character encoding' (although that's a big advance on calling it 'charset'). HTTP uses content-encoding. The two uses of the concept 'encoding' occur at different levels in the stack.

>> In consequence, using gzip content-encoding is compatible with +xml media types.

GK> For clarification: this would be the case only when a suitable MIME
GK> content-transfer-encoding header is applied, n'est pas? 

If its compressed on the fly, yes. If its stored compressed on the server, then Content-Encoding is used.

GK>  Otherwise such added
GK> encoding/decoding could be applied lower in the stack and not visible at the
GK> level of the MIME object.

GK> #g

 Chris Lilley          
 Interaction Domain Leader
 Co-Chair, W3C SVG Working Group
 W3C Graphics Activity Lead
 Co-Chair, W3C Hypertext CG