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Re: Wish for MathML 3: version attribute

From: Michael Kohlhase <m.kohlhase@jacobs-university.de>
Date: Sun, 16 Sep 2007 06:00:41 +0200
Message-ID: <46ECAA69.8020704@jacobs-university.de>
To: Bert Bos <bert@w3.org>
CC: www-math@w3.org, max@berger.name

Bert Bos wrote:
> Robert Miner wrote:
>> I also support this.  I don't think it will be controversial.
> Well...
> If we want MathML2 and 3 to co-exist (rather than recommend everybody to
> upgrade to 3) and the two versions require different implementations,
> then the difference should be expressed in the MIME type, by means of a
> new identifier or a parameter. Otherwise the client cannot tell the
> server what it supports and the server cannot give the client what it 
> needs.
I am not sure that this even applies to MathML practice, since almost 
always will MathML exist as MathML islands in another XML application. 
So are you suggesting something like application/xhtml1.1+mathml3+svg2.1 
? I think that a version attribute in the source makes sense, since then 
applications can tailor the behavior to old versions, somewhat like 
quirks mode in browsers.

> Even if the server only has one version of the document, it would be
> wasteful to send it to a client that in the end cannot handle it.
> Also, we have to see what existing version-2 clients do with a version
> attribute. If they don't stop on seeing the attribute but continue
> parsing anyway, the attribute has no use.
> Probably, there are also quite a few documents that would be valid in
> both MathML2 and MathML3, apart from that version attribute. The version
> attribute would require you to make one file for old clients and another
> for new ones. Keeping the version information outside the document
> avoids that.
> In general, version information (in whatever form) embedded in the
> document itself is not useful on the Web. Either the format has built-in
> forward and backward compatibility (old implementations can do something
> useful with new documents and vice versa), or it is in fact two
> different formats and their identifiers should be available as MIME
> types outside the document.
> HTML has long hesitated over this. The official specification has until
> now had version information in the document, but implementations ignored
> it. HTML5 therefore looks set to abandon the version info.
> CSS has never had version information and has always tried to be
> forwards and backwards compatible. Sometimes people ask for version
> information, but when questioned, it always turns out that what they
> really mean is a way to target a particular browser. Version info
> wouldn't help, because there is no specification that corresponds to a
> particular browser, if only because there is no specification that
> describes the bugs in browsers.
> (There is one counter-argument against new MIME types and that is that
> authors sometimes don't have control over the MIME types of their Web
> server, because their ISP is of too low quality. Some browsers therefore
> don't rely on the lesser known MIME types, but instead use content
> sniffing for commonly mislabeled types, i.e., they download the document
> and try to guess its type from the content.)
> I haven't made a list of the changes between version 2 and 3, but I'm
> hoping that we can avoid removing features (except for any that never
> worked in the first place) and can thus keep all existing MathML
> documents valid in version 3. The version 2 spec can then be declared
> obsolete and all software has to be upgraded, but all content can remain
> unchanged. There is more content than software and software has to be
> updated regularly anyway. There is no need for a new MIME type or a
> version parameter then.
> Bert

 Prof. Dr. Michael Kohlhase,       Office: Research 1, Room 62 
 Professor of Computer Science     Campus Ring 12, 
 School of Engineering & Science   D-28759 Bremen, Germany
 Jacobs University Bremen*         tel/fax: +49 421 200-3140/-493140
 m.kohlhase@jacobs-university.de http://kwarc.info/kohlhase 
 skype: m.kohlhase   * International University Bremen until Feb. 2007
Received on Sunday, 16 September 2007 04:01:04 UTC

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