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Stefan Ram wrote:
David Carlisle <david-news@xxxxxxxxxxxxxxxxxxxxx> writes:
That though is a restriction of DTD rather than of XML itself. Other XML
validation languages such as XSD or Relax NG Schema, or schematron for
exampes can all easily be used to constrain an attribute to be (for
example) a white space separated list of integer values.
You can also create a validation language that can be used to
constrain an attribute to be a valid Java program.
However, the structure of such an attribute is not being
described by the XML language anymore. The XML TR does not
describe the Java syntax. So it is not provided by the XML TR.
The XML TR describes a document made of elements and possibly
attributes. It provides rules and names for these structural parts.
XML provides rules and names for a list of IDREFs within an
attribute, so this still »is« XML.
But the XML TR does not provide rules and syntactical names
(nonterminal symbols) for a list of integer numerals (integer
literals) within an attribut.
This is another language. It might be call »Relax-XML« or so.
Such a valid Relax-XML document also can be a valid XML document.
Insofar it »is« XML. But XML does not describe a special
syntax for integer numerals within an attribute value. To XML,
this is just an opaque attribute value. Interpreting this as a
list of integers is not backed by the XML TR anymore, this needs
the additional Relax specification.
there are lots of things the XML spec doesn't secify, but to say XML
encoding lists of numbers (an SVG path attribute for example) isn't XML
is a rather strange conclusion to draw. For a start a lot (quite
possibly a majority) of XML is "just" well formed and not validated at
all so the relative expressive strengths of validation languages are
irrelevant. For documents that are to be validated, it's issentially
irrelevant to the end user, the internal organisation and timing of the
various working groups that mean that xml is split across a range of
specifications, xml itself, xml names, sax, dom, xsd etc. If you just go
by what's in the XML rec without relying on anything else, you can not
even use any standard parsing model, so use fo XML woul dbe rather hard,
or you may decide it's legal to use names like <a:b:c/> but then find
that the vast majority of current xml tools follow the additinal
constraints in the namespace spec and would reject such an element.
Actually even by your definition XML can do more than you imply: IDREFS
isn't the only list type NMTOKENS for example would allow you to specify
an attribute is a white space list of something, even if you can't, in
DTD, restrict the tokens further to be just digits. But to say XML with
lists of integers in an attribute isn't really XML because DTD can't
validate the XML is just like saying that an XMl document containing
english text isn't really XML because DTD can't enforce spell checking.
By that definition, what can XML be used for?
David
--
http://dpcarlisle.blogspot.com
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