Question

In my schema file below, I have an element Stat which extends Entity. As far as I am aware, I follow w3’s example, but when I go to parse the schema (and the xml that uses the schema) with through java’s DocumentBuilderFactory and SchemaFactory I get this exception:

org.xml.sax.SAXParseException; systemId: file:/schema/characterschema.xsd; 
    src-resolve.4.2: Error resolving component 'cg:Entity'. It was detected that
    'cg:Entity' is in namespace 'http://www.schemas.theliraeffect.com/chargen/entity',
    but components from this namespace are not referenceable from schema document
    'file:/home/andrew/QuasiWorkspace/CharacterGenerator/./schema/characterschema.xsd'.
    If this is the incorrect namespace, perhaps the prefix of 'cg:Entity' needs
    to be changed. If this is the correct namespace, then an appropriate 'import'
    tag should be added to '/schema/characterschema.xsd'.

So, it seems that I cannot see my namespace within my schema. Do I need to import my schema into itself or am I completely misreading this exception? Could it be that I am declaring my schema incorrectly?

This is my schema for reference:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
    xmlns:cg="http://www.schemas.theliraeffect.com/chargen/entity"
    elementFormDefault="qualified">

    <xs:element name="Entity">
        <xs:complexType>
            <xs:attribute name="id" type="xs:string" use="required"/>                    
            <xs:attribute name="name" type="xs:string"/>
            <xs:attribute name="description" type="xs:string"/>
        </xs:complexType>
    </xs:element>

    <xs:element name="Stat">
        <xs:complexType>
            <xs:complexContent>
                <xs:extension base="cg:Entity">
                    <xs:sequence>
                        <xs:element name="table" type="xs:string" minOccurs="0" maxOccurs="unbounded"/>                        
                    </xs:sequence>
                </xs:extension>
            </xs:complexContent>
        </xs:complexType>
    </xs:element>
</xs:schema>

Answer 1

There are two problems with your schema. First, you don’t declare a targetNamespace so the Entity and Stat elements you are defining are not in a namespace. Second, a type can’t extend an element, only another type.

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
    xmlns:cg="http://www.schemas.theliraeffect.com/chargen/entity"
    targetNamespace="http://www.schemas.theliraeffect.com/chargen/entity"
    elementFormDefault="qualified">

    <xs:complexType name="EntityType">
        <xs:attribute name="id" type="xs:string" use="required"/>                    
        <xs:attribute name="name" type="xs:string"/>
        <xs:attribute name="description" type="xs:string"/>
    </xs:complexType>

    <xs:element name="Entity" type="cg:EntityType" />


    <xs:complexType name="StatType">
        <xs:complexContent>
            <xs:extension base="cg:EntityType">
                <xs:sequence>
                    <xs:element name="table" type="xs:string" minOccurs="0"
                           maxOccurs="unbounded"/>                        
                </xs:sequence>
            </xs:extension>
        </xs:complexContent>
    </xs:complexType>

    <xs:element name="Stat" type="cg:StatType" />
</xs:schema>

Here I’m defining two types, one of which extends the other, and two top level elements of the respective types. All the top-level types and elements are defined into the targetNamespace of the schema, and the nested table element inside StatType is also in this namespace because of the elementFormDefault="qualified" – without this the Entity and Stat elements would be in the http://www.schemas.theliraeffect.com/chargen/entity namespace but the table element would be in no namespace.