xml-dev - Re: Last minute request for BASE64 section support in XML 1.0

["David G. Durand" <dgd@cs.bu.edu>]

	From: Deke Smith <deke@tallent.com>

	Don Park, donpark@quake.net said on 2/6/98 8:26 PM:

	>It looks like XML is about to be approved as standard by W3C.
Could we
	>please have BASE64 sections as a part of XML standard 1.0?
Everyone who
	>support this idea, please reply to this message (short replies
please to
	>avoid LISTRIVIA).

	Supported. If not officially accepted it WILL be used anyhow.

	Deke

This is silly. The specific proposal (a BASE64 marked section) _can't
be_ added at this point under the rules of the W3C. It's also unlikely
to fly in XML 1.1 for two reasons (which are more substantial
technical problems with the proposal as it stands):

  1. The proposed syntax is not compatible with SGML syntax, and can't
be made compatible without changes in SGML (violating the goals of the
XML project).

  2. The effect desired can be easily obtained in XML by the use of
NOTATION.

 For example:

<some-binary-element><![BASE64[ ..base64data..]]></some-binary-element>

could be replaced by (in the instance):
<some-binary-element>..base64data..</some-binary-element>

for a WF-checking application, the following DTD would be required:

<!attlist some-binary data-format NOTATION #FIXED "BASE64">

For validation, you'd have to declare the notation (by adding this to
the DTD or the internal subset):

<!NOTATION BASE64 "some URI for BASE64 encoding, determined by convention">

I may have made some detail mistakes, because I can't get to the
standard right now, but the basic point is that to handle base64
encoding (or any other encoding expressible in the XML character set)
you need only declare and attach a notation attribute.

If you don't like notation, you can even just use an attribute value
and keyword and skip the notation declaration. I don't remember the
character repertoire of BASE64, but the fact that it's email safe
means that the escaping issues are certainly no harer than those for
any XML text content.

If you really want to avoid escaping characters, you can use
references to external unparsed entities to avoid the problem altogether.


For the above reasons I expect that it _won't_ be used anyhow,
except by people who don't mind their documents being rejected by
conforming parsers. Given the presence of a simple way to do this
_inside_ XML, the need is unlikely to be regarded as being so
critical that conformance is irrelevant.

  -- David
------------------------------------------+----------------------------
David Durand                 dgd@cs.bu.edu| david@dynamicDiagrams.com
Boston University Computer Science        | Dynamic Diagrams
http://www.cs.bu.edu/students/grads/dgd/  | http://dynamicDiagrams.com/
                                          | MAPA: mapping for the WWW



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