XML Schema

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.w3schools.com" xmlns="http://www.w3schools.com" elementFormDefault="qualified">

<xs:element name="nokkis">
  <xs:complexType>
    <xs:sequence>

      <xs:element name="event" minOccurs="0" maxOccurs="unbounded">
        <xs:complexType>
          <xs:sequence>
            <xs:element name="name" type="xs:string" minOccurs="0" />
            <xs:element name="description" type="xs:string" minOccurs="0" />
            <xs:element name="startdate" type="xs:integer" minOccurs="0" />
            <xs:element name="enddate" type="xs:integer" minOccurs="0" />
            <xs:element name="num_tickets" type="xs:integer" minOccurs="0" />
            <xs:element name="max_tickets" type="xs:integer" minOccurs="0" />
            <xs:element name="barcode" type="xs:integer" minOccurs="0" maxOccurs="unbounded" />
            <xs:element name="apikey" minOccurs="0" maxOccurs="unbounded" >
              <xs:simpleType>
                <xs:restriction base="xs:string">
                  <xs:pattern value="[a-zA-Z0-9_]{1,30}"/>
                </xs:restriction>
              </xs:simpleType>
            </xs:element>
          </xs:sequence>
          <xs:attribute name="id" type="xs:integer" />
        </xs:complexType>
      </xs:element>
      
      <xs:element name="barcode" minOccurs="0" maxOccurs="unbounded">
        <xs:complexType>
          <xs:sequence>
            <xs:element name="event" type="xs:string" minOccurs="0" />
            <xs:element name="user" type="xs:string" minOccurs="0" />
            <xs:element name="status" type="xs:integer" minOccurs="0" />
            <xs:element name="valid" type="xs:integer" minOccurs="0" />
          </xs:sequence>
          <xs:attribute name="key" type="xs:integer" use="required" />
        </xs:complexType>
      </xs:element>
      
      <xs:element name="apikey" minOccurs="0" maxOccurs="unbounded">
        <xs:complexType>
          <xs:sequence>
            <xs:element name="name">
              <xs:simpleType>
                <xs:restriction base="xs:string">
                  <xs:pattern value="[a-zA-Z0-9_]{1,30}"/>
                </xs:restriction>
              </xs:simpleType>
            </xs:element>
            <xs:element name="event" type="xs:string" />
          </xs:sequence>
          <xs:attribute name="id" type="xs:integer" use="required" />
        </xs:complexType>
      </xs:element>   
      
      <xs:element name="action" minOccurs="0" maxOccurs="unbounded">
        <xs:complexType>
          <xs:sequence>
            <xs:element name="event" type="xs:string" minOccurs="0" />
            <xs:element name="barcode" type="xs:integer" minOccurs="0" />
            <xs:element name="apikey" minOccurs="0" >
              <xs:simpleType>
                <xs:restriction base="xs:string">
                  <xs:pattern value="[a-zA-Z0-9_]{1,30}"/>
                </xs:restriction>
              </xs:simpleType>
            </xs:element>
            <xs:element name="ip" type="xs:string" />
            <xs:element name="action_time" type="xs:integer" />
            <xs:element name="action_data">
              <xs:simpleType>
                <xs:restriction base="xs:string">
                  <xs:enumeration value="event_created" />
                  <xs:enumeration value="event_modified" />
                  <xs:enumeration value="barcode_created" />
                  <xs:enumeration value="barcode_used" />
                  <xs:enumeration value="barcode_failed" />
                  <xs:enumeration value="barcode_deleted" />
                </xs:restriction>
              </xs:simpleType>
            </xs:element>
          </xs:sequence>
          <xs:attribute name="id" type="xs:integer" use="required" />
        </xs:complexType>
      </xs:element>
      
      <xs:element name="error">
        <xs:complexType>
          <xs:simpleContent>
            <xs:extension base="xs:string">
              <xs:attribute name="id" type="xs:integer" />
            </xs:extension>
          </xs:simpleContent>
        </xs:complexType>
      </xs:element>       

    </xs:sequence>
  </xs:complexType>
</xs:element>

</xs:schema>