Creating Simple Types

Most of the types I've used in ch05_07.xsd are simple types that come built into the XML schema specification, such as xsd:string , xsd:integer , xsd:date , and so on. However, take a look at the attribute named bookID : this attribute is declared to be of the type catalogID :

 <xsd:complexType name="books">      <xsd:sequence>         <xsd:element name="book" minOccurs="0" maxOccurs="10">             <xsd:complexType>                 <xsd:sequence>                     <xsd:element name="bookTitle" type="xsd:string"/>                     <xsd:element name="pubDate" type="xsd:date" minOccurs='0'/>                  <xsd:element name="replacementValue" type="xsd:decimal"/>                    <xsd:element name="maxDaysOut">                        <xsd:simpleType>                            <xsd:restriction base="xsd:integer">                                <xsd:maxExclusive value="14"/>                            </xsd:restriction>                         </xsd:simpleType>                    </xsd:element>                </xsd:sequence>  <xsd:attribute name="bookID" type="catalogID"/>  </xsd:complexType>         </xsd:element>     </xsd:sequence> </xsd:complexType> 

This type, catalogID , is itself a simple type that is not built into the XML schema specification; instead, I've defined it with the <simpleType> element like this:

 <xsd:simpleType name="catalogID">      <xsd:restriction base="xsd:string">         <xsd:pattern value="\d{3}-\d{4}-\d{3}"/>     </xsd:restriction> </xsd:simpleType> 

Note in particular that you must base new simple types such as catalogID on already existing simple type (either a built-in simple type or one you've createdhere, I'm using the built-in xsd:string type). To do that, you use the base attribute in the <xsd:restriction> element. In the case of the catalogID type, I've based it on the xsd:string type with the attribute/value pair base="xsd:string" . To describe the properties of new simple types, XML schemas use facets.