More on notations and MIME types

W. Eliot Kimber eliot at
Thu Dec 3 20:28:47 GMT 1998

At 02:53 PM 12/3/98 -0500, John Cowan wrote:

>Here's my potted version of notations vs. MIME types:
>	Both provide names for syntactic encodings.
>	Notations have local names (private aliases),
>	whereas MIME types don't.
>	MIME type names have internal syntax, allowing partial
>	interpretation; notation names are opaque.

But you can get the same effect with data ("notation") attributes (or you
could, if XML had included them.).  Also, the SGML Extended facilities, we
formalized a mechanism for establishing notation hierarchies so that one
notation can name another notation as its supertype.  More verbose than the
MIME mechanism, but I think ultimately more flexible. Again, depends on
data attributes.  Here, I think, it comes down to syntax choices.  Any
syntax defined for compactness will almost always be limited in some key way.

And of course, you can combine notations with MIME types to take advantage
of the MIME facilities, if you want to (by making the MIME type the
external ID of the notation, directly or indirectly).

>	MIME types reference a central registry with private-use
>	extensions; notations reference a distributed registry.

But notations can use any central registry that exists, including the MIME
registry.  If we had a generally available public ID or URN registry, it
wouldn't even be an issue.

I observe that part of the issue here seems to be the need to have reliable
public registries for persistently-named resources, which is a general
problem.  MIME type names are persistent names--if there existed a
general-purpose registry of persistent names, then MIME type names wouldn't
need their own special-purpose registry (which obviously they had to have
in order to make MIME work at all).


<Address HyTime=bibloc>
W. Eliot Kimber, Senior Consulting SGML Engineer
ISOGEN International Corp.
2200 N. Lamar St., Suite 230, Dallas, TX 75202.  214.953.0004

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