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XML schema - multiple import of module

• From: "DUNN, Mark" <mark.dunn@oup.com>
• To: <xml-dev@lists.xml.org>
• Date: Thu, 4 Jun 2009 17:35:25 +0100

Hello,

I'm new to XML Schemas, and investigating conversion of a DTD to an XML
Schema. I have a problem describing the Schema version of the following
structure:

<doc>
 <div>
  <title>Section 1</title>
  <p>Some text...</p>
  <p>
   <law:extraxt>
    <title>Title of Regulation</title>
    <p>Text of regulation</p>
   </law:extract>
  </p>
 </div>
</doc>


The problem is in the non-namespaced <title> and <p> elements occurring
within the namespaced <law:extract> element. They are the same as the
ones occurring outside this element, so I'd like to define them only
once.

My attempt at expressing this structure uses three .xsd files:

main.xsd:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns="http://xsd.oup.com/ac-xsd/"
xmlns:law="http://xsd.oup.com/ac-law/"
targetNamespace="http://xsd.oup.com/ac-xsd/"
elementFormDefault="qualified">
	<xs:redefine schemaLocation="struct.xsd">
		<xs:group name="paragraph-content">
			<xs:choice>
				<xs:group ref="paragraph-content"/>
				<xs:element ref="law:extract"/>
			</xs:choice>
		</xs:group>
	</xs:redefine>
	<xs:import namespace="http://xsd.oup.com/ac-law/"
schemaLocation="law.xsd"></xs:import>
	...
</xs:schema>

law.xsd:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified"
targetNamespace="http://xsd.oup.com/ac-law/"
xmlns:law="http://xsd.oup.com/ac-law/"
xmlns:struct="http://xsd.oup.com/ac-xsd/">
	<xs:import schemaLocation="struct.xsd"
namespace="http://xsd.oup.com/ac-xsd/"></xs:import>
	<xs:element name="extract">
		<xs:complexType>
			<xs:sequence>
				<xs:element ref="struct:title"
minOccurs="0"/>
				<xs:element ref="struct:p"
minOccurs="1"/>
			</xs:sequence>
		</xs:complexType>
	</xs:element>
	...
</xs:schema> 


struct.xsd:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified" attributeFormDefault="unqualified"
targetNamespace="http://xsd.oup.com/ac-xsd/"
xmlns="http://xsd.oup.com/ac-xsd/">
	<xs:group name="general-inline">
		<xs:choice>
			<xs:element ref="b"/>
			<xs:element ref="i"/>
		</xs:choice>
	</xs:group>
	<xs:group name="paragraph-content">
		<xs:choice>
			<xs:group ref="general-inline"></xs:group>
			<!-- ... [plus others] ... --->
		</xs:choice>
	</xs:group>
	<xs:element name="p">
		<xs:complexType mixed="true">
			<xs:choice minOccurs="0" maxOccurs="unbounded">
				<xs:group ref="paragraph-content"/>
			</xs:choice>
		</xs:complexType>
	</xs:element>
	...
</xs:schema>


When I try saving the schema files in XMLSpy 2009, I get an error saying
that <title> is already declared, presumably because the file struct.xsd
has ben imported twice.

The W3C spec says that importing twice is legitimate, but vendors are
encouraged to raise it as an error. Fair enough - I don't like the
circularity in my description.

But the structure itself seems reasonable, I just can't see a way of
expressing it in XML Schema.

Can anyone help?


Kind regards,

Mark Dunn
XML Data Engineer
Oxford University Press

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