<schema xmlns="http://www.w3.org/2001/XMLSchema"
        xmlns:po="http://www.example.com/PO1"
        targetNamespace="http://www.example.com/PO1"
        elementFormDefault="unqualified"
        attributeFormDefault="unqualified">

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

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

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

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

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

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

</schema>

