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   Notations and MIME types

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  • From: John Cowan <cowan@locke.ccil.org>
  • To: XML Dev <xml-dev@ic.ac.uk>
  • Date: Thu, 09 Jul 1998 15:54:09 -0400

I will try to explain the issues in a way that both sides will find
intelligible.  There seem to be the following conceptual differences
between notations and MIME types:

1.  Notation names are normally declared locally, whereas MIME type
names have a global registry with a provision for local-use extensions.
This is resolved by noting that the NOTATION declaration provides
for a public ID and an URL (system id).  The system id of a
notation corresponding to a MIME type can refer to the URL
where the definition (in English) of the MIME type is stored.
A group of public IDs could also be manufactured of the
type "-//IETF//NOTATION MIME text/plain//EN", which would be
understood to be equivalent to the MIME type "text/plain".

2. Syntactically, MIME-types employ characters that aren't allowed
in public IDs or in XML Names.  This could be resolved by a mapping
convention.  The most important character in this respect is "/",
which is allowed in public ids but not in Names, since every
MIME type name has exactly one "/".

3.  There is a difference in expectation between the SGML style
and the Internet/MIME style about who declares what.  SGML systems
expect that referring documents will know the notation used by
objects that they refer to.  Internet documents such as mail
messages or Web pages, OTOH, usually simply refer to external
documents by URL, and expect either that the MIME type can be
guessed from the URL, or else that the remote system will return
the MIME type along with the content.  I don't know just what
should be done to smooth over this difference.

I hope this helps to clarify the issues.

John Cowan	http://www.ccil.org/~cowan		cowan@ccil.org
	You tollerday donsk?  N.  You tolkatiff scowegian?  Nn.
	You spigotty anglease?  Nnn.  You phonio saxo?  Nnnn.
		Clear all so!  'Tis a Jute.... (Finnegans Wake 16.5)

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