SAX and delayed entity loading

W. Eliot Kimber eliot at
Thu Dec 3 18:49:47 GMT 1998

At 01:21 PM 12/3/98 -0500, John Cowan wrote:
>> Notations are one
>> of the most underappreciated aspects of SGML.
>I agree in general.  But perhaps the indirection that (as you say)
>is so valuable in entities is really overkill in notations, given
>the large effort built up in assigning MIME types absolute names.

Unless I've misunderstood something, a MIME type is still an indirection to
the definition of that MIME type. I.e., "text/xml" is a pointer to the RFC
that establishes that MIME type. But then a problem is: where do I got to
figure out what RFC a given MIME type maps to?  What if the MIME type is an
"x-*" MIME type, what do I do then?  Note that the external ID for a
notation could, in theory be a MIME type:

<!NOTATION xml SYSTEM "urn:mime:text/xml" >

>> So saying that entities and notations are non-starters is, I think, a bit
>> strong.
>IMHO there has been insufficient effort on the part of tribal
>elders to explain what notations are meant to be for, and how
>they are useful to XMLists.  Elements and attributes (disregarding
>for the moment the perennial question when to use which) are well
>understood thanks to the HTML experience, but notations are not.

I've tried to do what I could.  It's clear that I need to write a paper
clearly outlining what notations are for and how they are best put to use.

The short answer is that they are a highly general way to associate data
objects with the definition of the rules that governs the interpretation of
that data object.  I think that the Web and Windows have established an
unreasonable expectation that software will "just know" how to deal with
things.  Unfortunately, you can't always rely on registered MIME types and
magic numbers.

Perhaps part of the problem is that in the Web world we have tended to
remove the need for such a generalized mechanism by hard-coding knowledge
of the semantics of everything?  But you can't do that forever, and MIME
only seems to make the problem worse by requiring that all interchangable
types be registered before they can be used. Notations don't require that
because the external ID of a notation can be anything (including MIME types
or their RFC documents).


<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

xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev at
Archived as:
To (un)subscribe, mailto:majordomo at the following message;
(un)subscribe xml-dev
To subscribe to the digests, mailto:majordomo at the following message;
subscribe xml-dev-digest
List coordinator, Henry Rzepa (mailto:rzepa at

More information about the Xml-dev mailing list