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Re: mime-type registration for WebCGM.

From: Thierry Michel <tmichel@w3.org>
Date: Mon, 24 Aug 2009 17:13:29 +0200
Message-ID: <4A92AE19.4050609@w3.org>
To: Lofton Henderson <lofton@rockynet.com>, WebCGM WG <public-webcgm-wg@w3.org>
Lofton,


I have asked Chris Lilley about the mime type registration as he was 
involved in the Registration Internet Media type for cgm, image/cgm in 
November 1995, and also with the SVG one.

he claims that we don't need a special mime type for GZIP compression 
.cgz files nor a new registration since WebCGM reuses the image/cgm 
registration and since gzip compression does not alter the Internet 
Media type.

Following is his response:


Chris Lilley wrote:
> On Monday, August 24, 2009, 2:48:55 PM, Thierry wrote:
> 
> TM> Hello,
> 
> TM> I would like to have some advice on  mime-type registration for WebCGM.
> 
> TM> Do we need a special mime type for GZIP compression .cgz files ?
> 
> No. After an early attempt to register a MIME type for gzip compression, there were then problems because two different media had the same MIME type (compressed PostScript and compressed VRML) so it wasn't possible to assign a single handler application to the one media type. So therefore, the actual media and the compression used, if any, were treated separately in Internet Mail and in HTTP.
> 
> So, the Internet Media type (mime type) is the same. However, the Transfer-Encoding or Content-Encoding will be different.
> 
> TM> [1] 
> TM> http://www.w3.org/TR/2009/WD-webcgm21-20090604/WebCGM21-Concepts.html#webcgm_2_4
> 
> Notice that the text at that URI could be read to imply that gzip compression can *only* be used over HTTP. (The SVG spec used to have similar woirding and was in fact so misunderstood, which is the origin of the Firefox bug that svgz only works when served over HTTP, not for local files. We fixed that wording in SVGT1.2 and have back ported it to the second edition of SVG 1.1).
> 
> TM> I looked up what Tiny 1.2 did about .svgz:
> TM> [2] http://www.w3.org/TR/SVGMobile12/intro.html#mimetype
> 
> TM> No apparent mention of svgz there, that I can see .
> 
> I think you missed
> 
> "(See Conformance Criteria for more information about gzip-compressed SVG files transmitted over HTTP.)"
> 
> which points to
> http://www.w3.org/TR/SVGMobile12/conform.html#ConformingSVGServers
> 
> which has the appropriate language about svgz and what headers to send for HTTP. You could copy that language for the WebCGM spec.
> 
> TM>   That [2] points to
> TM> this:
> TM> [3] http://www.w3.org/TR/SVGMobile12/mimereg.html
> 
> TM> Which points to this:
> TM> [4] http://www.w3.org/2002/06/registering-mediatype.html
> 
> TM> Do we need to register this mime-type using the new procedure, by draft
> TM> text within the REC or don't we ?
> 
> No.
> 
> The Internet Media type for cgm, image/cgm was registered in November 1995. (I helped with that registration).
> http://www.iana.org/assignments/media-types/image/cgm
> 
> All versions of CGM use the same media type but there are two mandatory parameters, version and ProfileId.
> 
> So you don't need a new registration, but you  do need to say what the values should be for version (I guess 4?) and profileID. Actually, you should say to use image/cgm, too (I couldn't see that in the WebCGM 2.0 spec).
> 
> Also, nowadays, "Security considerations: None" would raise a few eyebrows especially now that WebCGM has a DOM.
> 
> But all of that is a small section in the spec, and does not need a new registration since WebCGM reuses the image/cgm registration and since gzip compression does not alter the Internet Media type.
> 
> I'm happy for the entirety of this message to go to a Member of Public list, (either by forwarding, or post there and I will respond likewise).
> 
> 
> 
> 
Received on Monday, 24 August 2009 15:13:54 GMT

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