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RE: MIME types and file extensions for XML

• From: "Rick Jelliffe" <ricko@a...>
• To: <xml-dev@i...>
• Date: Mon, 8 Jun 1998 17:46:22 +1000

 
> From: owner-xml-dev@i...  

> The only question I have is that they're 
> registering text/xml and application/xml.  
> Are we expecting all XML-encoded 
> files to transfer under these two MIME types, 
> or will more specific MIME types emerge 
> for particular types of XML documents?

Anyone can make their own MIME type. The media
types have an extension mechanism. So if I made
"Rick's Markup Language"  I could use the media
type "application/x-rml". The "x-" prefix allows
user extension. 

Of course, if Robin Cover made up "Robin's Markup
Language" with the same type name, there is a 
potential problem.

This is the old "public identifier" problem. 
And the old solution is appropriate: the name should
include some owner name which will promote uniqueness.
If possible, this owner name should be from some 
registration authority.

In my case, I am pretty sure there is no one else
in the world with my name. So I can just say
something like "application/x-rick-jelliffe-ml"
and there will be no problems.  Robin Cover might
say "appplication/x-sil-org-sgml-ml" and use some
version of his internet domain name, since his 
name is less rare and there is slightly more chance
of collission (though still less!).

You can also apply to the IETF and get  your own
registration tree. So Microsoft, for example,
could apply for "ms": then they could have
"appplication/ms-rml". (But no-one has done this yet,
so it perhaps involves too much effort to be 
a viable alternative.)

(For more on this subject, see chapter 13 "Formal 
Public Identifiers" and chapter 14 "Data Content 
Notations" in my book. The RFCs for MIME media-type
registrations are useful too.)


Rick Jelliffe

==========================================================
The XML & SGML Cookbook, by Rick Jelliffe
Charles F. Goldfarb Series on Open Information Management
656 pages + CD-ROM, Prentice Hall 1998, ISBN 0-13-614223-0
http://www.sil.org/sgml/jelliffeXMLAnn.html
http://www.phptr.com/  > Book Search > "Jelliffe"
http://www.amazon.com/exec/obidos/ASIN/0136142230/002-4102466-3352420 

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