Re: mime-type registration for WebCGM.

Hi Chris,

Thanks for the feedback.  Here are some thoughts about your message.

First, we welcome that CGZ does not require a new media type registration.

We also disliked the too-strong connection between the gzip and HTTP 1.1 
usage.  We have removed that sentence, like SVG did.

Section 3.4 (which is in WebCGM 1.0 and 2.0) [1] does give the full media 
type specification for calling out CGM from an <object> element:

>The only standard way to reference inline CGMs from HTML documents is 
>through the object element, using the data attribute for the CGM file and 
>the type attribute to specify the full Mime Type. The minimal element for 
>adding CGM into a document would be:
><object data="xxx.cgm" type="image/cgm;Version=4;ProfileId=WebCGM" 
>width="200" height="100" />

On the other hand, the WebCGM spec intentionally says very little more 
about the registered MIME type.  The main reason is:

WebCGM, unlike SVG, intentionally does NOT standardize any normative 
conformance requirements for a general-purpose "WebCGM Server" conformance 
"Class of Product" (in the QAWG sense), and indeed we do not believe that 
IANA registration of CGM type, beyond use in the <object> tag, plays much 
of a role in our constituents' operational scenarios.

Therefore we would like minimize the in-text discussion of the details of 
the CGM MIME for a general purpose "WebCGM server", rather than spelling 
out the required usage parameters for those who might want consider such a 
configuration.

Thanks again, and we welcome any further thoughts you might have.

Regards,
-Lofton.

At 05:13 PM 8/24/2009 +0200, Thierry Michel wrote:
>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).