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9.6. XML Schema Document (XSD) File Sequencer

The XML Schema Document (XSD) File Sequencer can parse XML Schema Documents that adhere to the W3C's XML Schema Part 1 and Part 2 specifications, and output a representation of the XSD's attribute declarations, element declarations, simple type definitions, complex type definitions, import statements, include statements, attribute group declarations, annotations, other components, and even attributes with a non-schema namespace. This derived information is intended to accurately reflect the structure and semantics of the XSD files while also making it possible for users to easily navigate, query and search over this derived information. This sequencer captures the namespace and names of all referenced components, and will resolve references to components appearing within the same files.
The XML Schema specification is powerful, flexible, rich, and complicated. This means that many XML Schema Documents themselves are complicated. But it also means that there is a lot of variation in XSDs, and consequently there is a lot of variation in the output structure that this sequencer derives from XSD files.

9.6.1. XSD File Sequencer Example

Consider an example XML Schema Document taken from the XML Schema Primer : 
<?xml version="1.0" encoding="ISO-8859-1" ?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">

  <xsd:annotation>
    <xsd:documentation xml:lang="en">
     Purchase order schema for Example.com.
     Copyright 2000 Example.com. All rights reserved.
    </xsd:documentation>
  </xsd:annotation>

  <xsd:element name="purchaseOrder" type="PurchaseOrderType"/>

  <xsd:element name="comment" type="xsd:string"/>

  <xsd:complexType name="PurchaseOrderType">
    <xsd:sequence>
      <xsd:element name="shipTo" type="USAddress"/>
      <xsd:element name="billTo" type="USAddress"/>
      <xsd:element ref="comment" minOccurs="0"/>
      <xsd:element name="items"  type="Items"/>
    </xsd:sequence>
    <xsd:attribute name="orderDate" type="xsd:date"/>
  </xsd:complexType>

  <xsd:complexType name="USAddress">
    <xsd:sequence>
      <xsd:element name="name"   type="xsd:string"/>
      <xsd:element name="street" type="xsd:string"/>
      <xsd:element name="city"   type="xsd:string"/>
      <xsd:element name="state"  type="xsd:string"/>
      <xsd:element name="zip"    type="xsd:decimal"/>
    </xsd:sequence>
    <xsd:attribute name="country" type="xsd:NMTOKEN"
                   fixed="US"/>
  </xsd:complexType>

  <xsd:complexType name="Items">
    <xsd:sequence>
      <xsd:element name="item" minOccurs="0" maxOccurs="unbounded">
        <xsd:complexType>
          <xsd:sequence>
            <xsd:element name="productName" type="xsd:string"/>
            <xsd:element name="quantity">
              <xsd:simpleType>
                <xsd:restriction base="xsd:positiveInteger">
                  <xsd:maxExclusive value="100"/>
                </xsd:restriction>
              </xsd:simpleType>
            </xsd:element>
            <xsd:element name="USPrice"  type="xsd:decimal"/>
            <xsd:element ref="comment"   minOccurs="0"/>
            <xsd:element name="shipDate" type="xsd:date" minOccurs="0"/>
          </xsd:sequence>
          <xsd:attribute name="partNum" type="SKU" use="required"/>
        </xsd:complexType>
      </xsd:element>
    </xsd:sequence>
  </xsd:complexType>

  <!-- Stock Keeping Unit, a code for identifying products -->
  <xsd:simpleType name="SKU">
    <xsd:restriction base="xsd:string">
      <xsd:pattern value="\d{3}-[A-Z]{2}"/>
    </xsd:restriction>
  </xsd:simpleType>

</xsd:schema>
This schema defines the structure of several XML elements used to represent purchase orders, and describes an XML document such as the following: 
<?xml version="1.0"?>
<purchaseOrder orderDate="1999-10-20">
   <shipTo country="US">
      <name>Alice Smith</name>
      <street>123 Maple Street</street>
      <city>Mill Valley</city>
      <state>CA</state>
      <zip>90952</zip>
   </shipTo>
   <billTo country="US">
      <name>Robert Smith</name>
      <street>8 Oak Avenue</street>
      <city>Old Town</city>
      <state>PA</state>
      <zip>95819</zip>
   </billTo>
   <comment>Hurry, my lawn is going wild<!/comment>
   <items>
      <item partNum="872-AA">
         <productName>Lawnmower</productName>
         <quantity>1</quantity>
         <USPrice>148.95</USPrice>
         <comment>Confirm this is electric</comment>
      </item>
      <item partNum="926-AA">
         <productName>Baby Monitor</productName>
         <quantity>1</quantity>
         <USPrice>39.98</USPrice>
         <shipDate>1999-05-21</shipDate>
      </item>
   </items>
</purchaseOrder>

9.6.2. XSD File Sequencer Node Types

The XSD sequencer follows JCR best-practices by defining all nodes to have a primary type that allows any single or multi-valued property, meaning it is possible and valid for any node to have any property (with single or multiple values). In fact, this feature is used when XSD files contain attributes with non-schema namespaces, which are then mapped onto properties with the attributes name and possibly-empty namespace. However, it is still useful to capture the metadata about what that node represents, and so the sequencer use explicit node type definitions and mixins for this.

9.6.3. Using the XSD File Sequencer

To use the XSD File Sequencer, include the appropriate version of the Maven artifact with a org.modeshape group ID and modeshape-sequencer-xsd artifacts ID. Alternatively, if you are using JAR files and manually setting up the classpath for your application, use the modeshape-sequencer-xsd-2.7.0.Final-jar-with-dependencies.jar file. Then, define a sequencing configuration, using something similar to this: 
{
    "name" : "XSD Sequencer Test Repository",
    "sequencing" : {
        "removeDerivedContentWithOriginal" : true,
        "sequencers" : {
            "XSD Sequencer" : {
                "classname" : "xsdsequencer",
                "pathExpressions" : [ "default:/(*.xsd)/jcr:content[@jcr:data]" ]
            }
        }
    }
}