xml-dev - Data attributes (was: Stylesheets considered limiting)

[John Cowan <cowan@locke.ccil.org>]

W. Eliot Kimber wrote:

> Sure.

Thank you.  Your writeup is very clear as always.
 
> <!NOTATION gif SYSTEM "ftp://ftp.isi.edu/">
> <!ATTLIST #NOTATION gif
>    width CDATA "100"
>    height CDATA "100">
> 
> <!ENTITY big-graphic SYSTEM "picture.gif" NDATA gif
>   [ width="640" height="480"]>

Okay.  Since XML cannot have references to unparsed entities*, the
above can be treated as syntactic sugar.  Specifically,

	<GRAPHIC pic="big-graphic"/>

is effectively syntactic sugar for:

	<GRAPHIC pic="big-graphic" gif.width="640" gif.height="480"/>

but bypassing the SGML/XML restriction that the validity or invalidity
of attributes cannot depend on the values of other attributes.
If "big-picture" were not a "gif" entity, the "gif.width" and
"gif.height" attributes would be invalid.

It would be very easy to create a ParserFilter on top of a
validating XML parser (so that we reliably get attribute types)
that processed the above declarations (wrapped in PIs)
and generated extra attributes of the type shown above.

*(Come to think of it, references to unparsed entities could be
seen as syntactic sugar for an anonymous empty element with a
single anonymous ENTITY attribute.)

> <!ATTLIST SelectData
>    notation NOTATION(MyQuery) MyQuery
>    table CDATA #REQUIRED
>    select-on CDATA #REQUIRED
>    where (name|ssnum|phone) #REQUIRED>

In this case, though, the notation attributes seem to blend with
the regular attributes, and are redeclared in the ATTLIST declaration
for the element.  What happens in the case of an element type that
can be governed by alternative notations?

-- 
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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