xml-dev - RE: <!NOTATION>

["Matthew Sergeant (EML)" <Matthew.Sergeant@eml.ericsson.se>]

> -----Original Message-----
> From:	John Cowan [SMTP:cowan@locke.ccil.org]
> 
> Let's say that you have an element with #PCDATA content that's
> supposed to contain a date, like this:
> 
> 	<CREATED>1999-01-21</CREATED>
> 
> You can say that this is a date in a standard way by adding the
> following to the DTD:
> 
> 	<!NOTATION ISO-8601-date SYSTEM "http://www.iso.ch/8601">
> 	<!ATTLIST CREATED
> 		type NOTATION(ISO-8601-date) #FIXED "ISO-8601-date">
> 
> which says that all CREATED elements have an attribute named "type",
> of type NOTATION, with fixed value "ISO-8601-date", which is a
> notation bound to the ISO 8601 definition of a date.  This notation
> is verbose because there's flexibility in it which I'm not really
> exercising, to have elements whose content can be one of multiple
> datatypes, like:
> 
> 	<!NOTATION int32 SYSTEM "...">
> 	<!NOTATION int64 SYSTEM "....">
> 	<!NOTATION float SYSTEM "......">
> 	<!ATTLIST MUTABLE
> 		type NOTATION(int32,int64,float) #REQUIRED>
> 
> which declares that MUTABLE elements must have a "type" attribute
> whose value is either "int32" or "int64" or "float", and the notation
> declarations tell you what those mean.  The systemids are
> URLs that point to the definition of the datatype (in English or
> whatever language natural or formalized).
> 
	Unfortunately that information is only really useful for document
authors (which is fine, in itself) - it doesn't appear (to me) to be any use
to parsers. It can be of /some/ use to custom parser code, but only when
that code has prior knowledge of these notation definitions. And that's a
shame. Perhaps we need some standard notations?

	Matt.

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