Modifying an XML Schema with XSLT

Posted on 3 June 2009 by Pascal Alma

Recently I ran into an issue with a XSD that I had generated by using our modelling tool. It appeared the XSD did not match with my wishes so I had to modify the XSD. Now I could do this by hand quite easily but that would mean I had to redo it every time I regenerated the XSD after a model change. So I decided to use XSLT for the modifications. I have used XSLT quite extensively at previous projects but these where about 8 years ago and it just made me realize how fast one looses his knowledge if you don’t use it anymore.
Anyway, to avoid this situation for the next few years I decided to post about the basics of XSLT that I used in this situation so I always have a reference to get back at. The situation was that an XSD was generated but it was lacking several things:

  • no use of namespaces (both import and prefixes)
  • names of custom defined types didn’t end with the suffix ‘Type’
  • some complex types were missing

And several more things but the idea stays the same.
Here is an example XSD that could be generated by the tool:

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<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
	<xs:complexType name="Address">
		<xs:sequence>
			<xs:element name="street" type="xs:string"/>
			<xs:element name="nr" type="xs:integer"/>
			<xs:element name="postalCode" type="myPostalCode"/>
		</xs:sequence>
	</xs:complexType>
	<xs:complexType name="Customer">
		<xs:sequence>
			<xs:element name="firstName" type="xs:string" minOccurs="0"/>
			<xs:element name="lastName" type="xs:string"/>
			<xs:element name="address" type="Address"/>
		</xs:sequence>
	</xs:complexType>
</xs:schema>

Here is how I would like the XSD to be look like:

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<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:tns="htpp://www.redstream.nl/customer" xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="htpp://www.redstream.nl/customer">
	<xs:element name="customer" type="tns:CustomerType"/>
	<xs:complexType name="AddressType">
		<xs:sequence>
			<xs:element name="street" type="xs:string"/>
			<xs:element name="nr" type="xs:integer"/>
			<xs:element name="postalCode" type="tns:myPostalCodeType"/>
		</xs:sequence>
	</xs:complexType>
	<xs:complexType name="CustomerType">
		<xs:sequence>
			<xs:element name="firstName" type="xs:string" minOccurs="0"/>
			<xs:element name="lastName" type="xs:string"/>
			<xs:element name="address" type="tns:AddressType"/>
		</xs:sequence>
	</xs:complexType>
	<xs:complexType name="myPostalCodeType">
		<xs:sequence>
			<xs:element name="firstPart">
				<xs:simpleType>
					<xs:restriction base="xs:string">
						<xs:length value="4"/>
					</xs:restriction>
				</xs:simpleType>
			</xs:element>
			<xs:element name="secondPart">
				<xs:simpleType>
					<xs:restriction base="xs:string">
						<xs:length value="2"/>
					</xs:restriction>
				</xs:simpleType>
			</xs:element>
		</xs:sequence>
	</xs:complexType>
</xs:schema>

To get to this last XSD I used the following XSLT (see inline documentation for explanation):

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<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xs="http://www.w3.org/2001/XMLSchema">
	<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>
	<!-- first copy the root and apply templates-->
	<xsl:template match="/">
		<xsl:copy>
			<!-- copy the attributes (if any) of the root element -->
			<xsl:copy-of select="@*"/>
			<xsl:apply-templates/>
		</xsl:copy>
	</xsl:template>
	<!-- match any other element and copy it with the attributes -->
	<xsl:template match="*">
		<xsl:copy>
			<xsl:copy-of select="@*"/>
			<xsl:apply-templates/>
		</xsl:copy>
	</xsl:template>
	<!-- Add the necessary namespaces to the root of the schema -->
	<xsl:template match="xs:schema">
		<!-- Recreate the xs:schema element-->
		<xsl:element name="xs:schema">
			<!-- Copy the existing attributes in the original xs:schema element to this one -->
			<xsl:copy-of select="@*"/>
			<!-- add Namespace -->
			<xsl:namespace name="tns">htpp://www.redstream.nl/customer</xsl:namespace>
			<xsl:attribute name="targetNamespace">htpp://www.redstream.nl/customer</xsl:attribute>
			<!-- add toplevel element -->
			<xsl:element name="xs:element">
				<xsl:attribute name="name">customer</xsl:attribute>
				<xsl:attribute name="type">tns:CustomerType</xsl:attribute>
			</xsl:element>
			<!-- continue with matching al child elements of the xs:schema element-->
			<xsl:apply-templates/>
			<!-- call a custom template to add an extra complexType to the schema that couldn't be generated by the modelling tool-->
			<xsl:call-template name="addPostalCodeType"/>
		</xsl:element>
	</xsl:template>
	<!-- suffix all complexType names with 'Type' -->
	<xsl:template match="xs:complexType">
		<xsl:choose>
			<!-- Check if the type already has the suffix 'Type' -->
			<xsl:when test="substring(@name, (string-length(@name)-3)) = 'Type'">
				<!-- if so, just copy the existing attributes -->
				<xsl:copy>
					<xsl:copy-of select="@*"/>
					<xsl:apply-templates/>
				</xsl:copy>
			</xsl:when>
			<xsl:otherwise>
				<!-- if not, copy all attribute and overwrite the attribute 'name' so the suffix 'Type' is added-->
				<xsl:copy>
					<xsl:copy-of select="@*"/>
					<xsl:attribute name="name"><xsl:value-of select="@name"/>Type</xsl:attribute>
					<xsl:apply-templates/>
				</xsl:copy>
			</xsl:otherwise>
		</xsl:choose>
	</xsl:template>
	<!-- Prefix all types with 'tns:'. All default xs: types are untouched.    -->
	<xsl:template match="xs:element">
		<!-- Create a variable with the name of the type of the element in it. It appears this 'type' attribute
			can be of different types so take this into account -->
		<xsl:variable name="elementType">
			<xsl:choose>
				<xsl:when test="@type instance of xs:string or @type instance of xs:untypedAtomic">
					<xsl:choose>
						<xsl:when test="contains(@type,':')">
							<xsl:value-of select="substring-after(@type,':')"/>
						</xsl:when>
						<xsl:otherwise>
							<xsl:value-of select="@type"/>
						</xsl:otherwise>
					</xsl:choose>
				</xsl:when>
				<xsl:otherwise>
					<xsl:value-of select="@type"/>
				</xsl:otherwise>
			</xsl:choose>-->
		</xsl:variable>
		<!-- Create a variable with the namespace prefix of the attribute if any. -->
		<xsl:variable name="elementTypePrefix">
			<xsl:choose>
				<xsl:when test="@type instance of xs:QName">
					<xsl:value-of select="prefix-from-QName(@type)"/>
				</xsl:when>
				<xsl:when test="@type instance of xs:string">
					<xsl:value-of select="substring-before(@type,':')"/>
				</xsl:when>
			        <xsl:otherwise>
                                       <xsl:value-of select="substring-before(@type,':')"/>
                                </xsl:otherwise>
			</xsl:choose>
		</xsl:variable>
		<!-- Now the variables are filled we can use it to determine if we need to add a prefix -->
		<xsl:choose>
			<!-- if type starts with xs: the prefix must not be changed -->
			<xsl:when test="$elementTypePrefix = 'xs'">
				<xsl:copy>
					<xsl:copy-of select="@*"/>
					<xsl:apply-templates/>
				</xsl:copy>
			</xsl:when>
			<xsl:otherwise>
				<xsl:copy>
					<xsl:copy-of select="@*"/>
					<!-- A few steps back we renamed complextypes so they ended with 'Type'. Now we have to suffix the places
              where the types are reffered also with 'Type' -->
					<xsl:if test="substring($elementType, (string-length($elementType)-3)) != 'Type'">
						<xsl:attribute name="type">tns:<xsl:value-of select="@type"/>Type</xsl:attribute>
					</xsl:if>
					<xsl:if test="substring($elementType, (string-length($elementType)-3)) = 'Type'">
						<xsl:attribute name="type">tns:<xsl:value-of select="@type"/></xsl:attribute>
					</xsl:if>
					<xsl:apply-templates/>
				</xsl:copy>
			</xsl:otherwise>
		</xsl:choose>
	</xsl:template>
	<!-- The next template generates the complexType 'myPostalCodeType' when the template is called -->
	<xsl:template name="addPostalCodeType">
		<xsl:element name="xs:complexType">
			<xsl:attribute name="name">myPostalCodeType</xsl:attribute>
			<xsl:element name="xs:sequence">
				<xsl:element name="xs:element">
					<xsl:attribute name="name">firstPart</xsl:attribute>
					<xsl:element name="xs:simpleType">
						<xsl:element name="xs:restriction">
							<xsl:attribute name="base">xs:string</xsl:attribute>
							<xsl:element name="xs:length">
								<xsl:attribute name="value">4</xsl:attribute>
							</xsl:element>
						</xsl:element>
					</xsl:element>
				</xsl:element>
				<xsl:element name="xs:element">
					<xsl:attribute name="name">secondPart</xsl:attribute>
					<xsl:element name="xs:simpleType">
						<xsl:element name="xs:restriction">
							<xsl:attribute name="base">xs:string</xsl:attribute>
							<xsl:element name="xs:length">
								<xsl:attribute name="value">2</xsl:attribute>
							</xsl:element>
						</xsl:element>
					</xsl:element>
				</xsl:element>
			</xsl:element>
		</xsl:element>
	</xsl:template>
</xsl:stylesheet>

Although this example might be very specific and there are better ways to obtain similar results, to me this might be a handy reminder how to solve an issue with XSLT and perhaps it might even help you in some way. In another post I will show how I do this translation in Maven and also validate the outcome.

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About Pascal Alma

Pascal started as an Oracle Developer in 1997 and developed numerous applications with Oracle Designer/Developer and PL/SQL. Since 2001 Pascal becomes more and more active with the development of software at the Java/J2EE platform. Nowadays Pascal is a senior JEE Developer/ Architect and has a lot of experience with several open source initiatives/ frameworks especially within the Enterprise Integration area. Besides these technical skills Pascal is a big Scrum enthusiastic.

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