Importing Schemas with No Namespaces (XML Schema)

10.9. Importing Schemas with No Namespaces

We have seen how we can reference components from other namespaces and how the elements and attributes included in these components keep their full name, namespaces, and form (in Section 10.3, "To Qualify Or Not to Qualify?"). However, this mechanism has a restriction: you can only reference global elements and attributes, and global elements and attributes must always be qualified.

Therefore, the only solution to importing elements and attributes with no namespace is to import a schema without any target namespace. Let's say that we want to describe a document in which the vocabulary to describe people has no namespace:

<?xml version="1.0"?>
<lib:library xmlns:lib="http://dyomedea.com/ns/library">
  <lib:book id="b0836217462">
    <lib:title>
      Being a Dog Is a Full-Time Job
    </lib:title>
    <lib:authors>
      <person id="CMS">
        <name>
          Charles M Schulz
        </name>
      </person>
    </lib:authors>
  </lib:book>
</lib:library>

The import of the schema without a namespace is done exactly as we've seen earlier with schemas having target namespaces, except now we omit the namespace attribute. Another point to note is that to be able to reference the components from the schema you are including, you will have to keep the default namespace (unprefixed) available:

<?xml version="1.0"?> 
<xs:schema targetNamespace="http://dyomedea.com/ns/library"
  elementFormDefault="qualified" attributeFormDefault="unqualified"
  xmlns:lib="http://dyomedea.com/ns/library"
  xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:import schemaLocation="very-simple-2-ns-ppl-nons.xsd"/>
  <xs:element name="library">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="book" type="lib:bookType"/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
  <xs:complexType name="bookType">
    <xs:sequence>
      <xs:element name="title" type="xs:string"/>
      <xs:element name="authors">
        <xs:complexType>
          <xs:sequence>
            <xs:element ref="person"/>
          </xs:sequence>
        </xs:complexType>
      </xs:element>
    </xs:sequence>
    <xs:attribute name="id" type="xs:ID" use="required"/>
  </xs:complexType>
</xs:schema>

The included schema is:

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="person" type="personType"/>
  <xs:complexType name="personType">
    <xs:sequence>
      <xs:element name="name" type="xs:string"/>
    </xs:sequence>
    <xs:attribute name="id" type="xs:ID" use="required"/>
  </xs:complexType>
</xs:schema>

In this case, all the components are considered unqualified. All the other behavior, including the difference between referencing elements or attributes and using datatypes, is relevant.

We see then that to define unqualified elements and attributes in a schema with a target namespace, we have to choose between defining them locally in the schema or defining them in a separate schema without an imported target namespace.