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   Re: [xml-dev] Syntax vs semantics

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The use of substitution groups in a schema doesn't mean you're straying
dangerously over the syntax-semantics boundary.  It just means that
the _syntax_ of a number of your elements has something in common.  If
I write:

<xs:element name="para">
 <xs:complexType mixed="true">
   <xs:element ref="decoration" minOccurs="0" maxOccurs="unbounded"/>

<xs:element name="decoration" abstract="true" type="subDeco"/>

<xs:complexType name="subDeco" mixed="true">
  <xs:element ref="coreDecoration" minOccurs="0" maxOccurs="unbounded"/>

<xs:element name="coreDecoration" abstract="true" type="xs:string/>

<xs:element name="strong" substitutionGroup="decoration"/>

<xs:element name="quote" substitutionGroup="decoration"/>

<xs:element name="emph" substitutionGroup="coreDecoration"/>

in order to validate things such as

<para>This is a review of <strong>The <emph>Last</emph>
Emperor</strong>, in which we find the lead character saying <quote>I
<emph>will</emph> go to the ball!</quote>.</para>

there's nothing particular semantic about the use substitution group,
except in so far as one expects semantics to follow syntax to some
extent in _any_ coherent document type.

I'm just using the s-g mechanism to capture common patterning of the
relevant elements, and to make it easy to extend my document type by
adding more decorations in the future.

  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
                      Half-time member of W3C Team
     2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
	    Fax: (44) 131 650-4587, e-mail: ht@cogsci.ed.ac.uk
		     URL: http://www.ltg.ed.ac.uk/~ht/
 [mail really from me _always_ has this .sig -- mail without it is forged spam]


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