Binary Data in XML : Turning back the clock
W. Eliot Kimber
eliot at dns.isogen.com
Wed Sep 30 20:05:55 BST 1998
At 09:54 AM 9/30/98 -0700, Tim Bray wrote:
>At 12:34 PM 9/30/98 -0400, david at megginson.com wrote:
>>Quite right. Right now, XML 1.0 has notations for this purpose, as
>>Eliot keeps reminding us; it would also be possible to invent a
>>standard attribute like 'xml:content', for use whether or not an
>>element's content was Base64-encoded:
>Yeah, but NOTATIONs require the use of a validating processor, and
>lots of non-validating apps would like to use base64. Having said
>that, I think that your proposed xml:content is more or less exactly
>what NOTATION is for? -Tim
<xml-dev at ic.ac.uk>
Notations don't require validating parsers, they only require parsers that
read and understand notation declarations. But they also require that there
be a DOCTYPE declaration so you can specify the notation declaration.
In this case, I think that a conventialized attribute would be sufficient,
but a notation of the same name as the value of the attribute should be
interpreted in the same way.
Or, said another way, an "xml:content" attribute could be presumed to be
declared with a value prescription of "NOTATION". The notation declaration
for the named notation is then implied.
This is analogous to "PI targets", where the spec says that the PI target
name is, semantically, the name of a notation, but you don't have to
declare the notation if you don't feel like it, but if there is a notation
declared with that name, it's rules govern the interpretation of the PI.
It would, I think, make sense to say the same thing for this.
And note that the notation of the data is, as previously mentioned,
orthoganal to how that data is encoded in the source document. Therefore,
you would not expect to have a notation of "base64".
Of course, if XML had data attributes, you could define a conventional data
attribute that specified the instance encoding, allowing different
notations to define what encodings their processors should support, but
nobody ever listens to me....
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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