How to prevent double elements when merging include files in xsd? - xslt

Question

I am working on a stylesheet that processes some XSDs.
The main XSD file includes 2 others. Of those 2 one also includes the other.
All XSDs have the same attributes and namespaces in the root element. The files are only separate for maintenance purposes.
The stylesheet:
<?xml version="1.0" encoding="ISO-8859-1"?>
<xsl:stylesheet
version="2.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:exa="http://www.example.com/"
exclude-result-prefixes="xsl xs exa">
<xsl:output method="xml" indent="yes" encoding="iso-8859-1" />
<!-- global variable to merge schema with it's includes
to be used for further processing the schema -->
<xsl:variable name="with_includes">
<xsl:apply-templates select="/xs:schema" mode="include"/>
</xsl:variable>
<!-- copy the main schema root element including attributes
then process all nodes in it -->
<xsl:template match="xs:schema" mode="include">
<xsl:copy>
<xsl:copy-of select="#*"/>
<xsl:apply-templates select="node()" mode="include"/>
</xsl:copy>
</xsl:template>
<!-- all schemas have the same namespaces and targetnamespace defined
so do not copy namespaces -->
<xsl:template match="node()" mode="include">
<xsl:copy-of select="." copy-namespaces="no"/>
</xsl:template>
<!-- when matching an include, process all the nodes in the schema -->
<xsl:template match="xs:include" mode="include">
<xsl:apply-templates select="doc(#schemaLocation)/xs:schema/node()" mode="include"/>
</xsl:template>
<!-- only here to show the result -->
<xsl:template match="/xs:schema">
<xsl:copy-of select="$with_includes"/>
</xsl:template>
</xsl:stylesheet>
Some very basic example schemas to demonstrate the problem:
Schema A.xsd:
<?xml version="1.0" encoding="ISO-8859-1"?>
<xs:schema
attributeFormDefault="unqualified"
elementFormDefault="qualified"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://www.example.com/example"
xmlns:exa="http://www.example.com/example">
<xs:include schemaLocation="B.xsd"/>
<xs:include schemaLocation="C.xsd"/>
<xs:element name="a" type="exa:t_a"/>
<xs:complexType name="t_a">
<xs:sequence>
<xs:element name="b" type="exa:t_b"/>
<xs:element name="c" type="exa:t_c"/>
</xs:sequence>
</xs:complexType>
</xs:schema>
Schema B.xsd:
<?xml version="1.0" encoding="ISO-8859-1"?>
<xs:schema
attributeFormDefault="unqualified"
elementFormDefault="qualified"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://www.example.com/example"
xmlns:exa="http://www.example.com/example">
<xs:include schemaLocation="C.xsd"/>
<xs:complexType name="t_b">
<xs:sequence>
<xs:element name="c1" type="exa:t_c"/>
<xs:element name="c2" type="exa:t_c"/>
</xs:sequence>
</xs:complexType>
</xs:schema>
Schema C.xsd
<?xml version="1.0" encoding="ISO-8859-1"?>
<xs:schema
attributeFormDefault="unqualified"
elementFormDefault="qualified"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://www.example.com/example"
xmlns:exa="http://www.example.com/example">
<xs:simpleType name="t_c">
<xs:restriction base="xs:string">
<xs:minLength value="1"/>
<xs:maxLength value="20"/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
If I use the stylesheet above, I get simpleType t_c twice in the result. I am looking for a way to prevent that.
Btw, I use Saxon.

Answer 1

Deduplicating the includes is relatively straightforward, but it becomes more complex if you need to handle cycles as well - cycles of xs:includes are permitted in XSD, though the 1.0 spec isn't entirely clear on the point. If you're not concerned about cycles, just build a list of all the includes by transitive expansion using a recursive function, preferably calling resolve-uri() to resolve each #schemaLocation against its base URI, then remove duplicates from the list using distinct-values(). If you need to eliminate cycles, you'll need to pass a parameter to your recursive function indicating the route by which the document was reached, and ignore a document if it's already on the list. If you've got a copy of my book, there's an example of cycle detection in the section on xsl:call-template. But you may find the book too expensive too ;-(