Extending Types in xml schema

["Craig Edmunds" <craig.edmunds@comtec-europe.co.uk>]

I'm having problems adding elements to a choose group in the base type, from my new type:


Base Type:

	<xs:complexType name="textBaseType" mixed="true">
		<xs:annotation>
			<xs:documentation>
			Base class for text based objects, although the schema
			allows you to use this class directly, DON'T!  This is simply a base class- unfortunately
			xml schema has no way of declaring "private" types (as far as i know).
			</xs:documentation>
		</xs:annotation>
		<xs:choice minOccurs="0" maxOccurs="unbounded">
			<xs:element name="br"/>
			<xs:element name="p" type="textBaseType"/>
			<xs:element name="span" type="spanType"/>
			<xs:element name="ul" type="ulType"/>
			<xs:element name="table" type="tableType"/>
		</xs:choice>
	</xs:complexType>


Derived Type:

	<xs:complexType name="spanType" mixed="true">
		<xs:complexContent mixed="true">
			<xs:extension base="textBaseType">
				<xs:annotation>
					<xs:documentation/>
				</xs:annotation>
				<xs:choice minOccurs="0" maxOccurs="unbounded">
					<xs:element name="li" type="tableType"/>
				</xs:choice>
			</xs:extension>
		</xs:complexContent>
	</xs:complexType>

I understand that this would actually be represented as

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"; elementFormDefault="qualified" attributeFormDefault="unqualified">
	<xs:complexType name="spanType" mixed="true">
		<xs:annotation>
			<xs:documentation/>
		</xs:annotation>
		<xs:sequence>
			<xs:choice minOccurs="0" maxOccurs="unbounded">
				<xs:element name="br"/>
				<xs:element name="p" type="textBaseType"/>
				<xs:element name="span" type="spanType"/>
				<xs:element name="ul" type="ulType"/>
				<xs:element name="table" type="tableType"/>
			</xs:choice>
			<xs:choice minOccurs="0" maxOccurs="unbounded">
				<xs:element name="li" type="tableType"/>
			</xs:choice>
		</xs:sequence>
	</xs:complexType>
</xs:schema>

And that is obviously wrong.  I have heard substitution groups mentioned but i haven't managed to find any good tutorials (there's only about 1/2 a page in Definitive XML Schema!).

Any Tips?

Cheers
c


==================================== 
Craig Edmunds 
Web Developer
Comtec (Europe) Ltd
==================================== 
t: +44 (0)1633 627500
f: +44 (0)1633 627501 
e: craig.edmunds@comtec-europe.co.uk
w: www.comtec-europe.co.uk

6th Floor Gwent House, Gwent Square 
Cwmbran, South Wales, NP44 1PL 
===================================



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