xmlns:ann="http://relaxng.org/ns/compatibility/annotations/1.0"

         datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">

  <start>

      <ref name="element-rule"/>

  </start>

  <define name="element-rule">

    <element name="rule">

     <choice>

     <attribute name="id-ref"><data type="IDREF"/></attribute>

     <group>

      <attribute name="id"><data type="ID"/></attribute>

      <choice>

        <externalRef href="score.rng"/>

        <attribute name="score-attribute"><text/></attribute>

      </choice>

      <optional>

        <attribute name="boolean-op">

          <choice>

            <value>or</value>

            <value>and</value>

          </choice>

        </attribute>

      </optional>

      <optional>

        <attribute name="role"><text/></attribute>

      </optional>

      <oneOrMore>

        <choice>

          <element name="expression">

            <attribute name="id"><data type="ID"/></attribute>

            <attribute name="attribute"><text/></attribute>

            <attribute name="operation">

              <choice>

                <value>lt</value>

                <value>gt</value>

                <value>lte</value>

                <value>gte</value>

                <value>eq</value>

                <value>ne</value>

                <value>defined</value>

                <value>not_defined</value>

              </choice>

            </attribute>

            <optional>

              <attribute name="value"><text/></attribute>

            </optional>

            <optional>

              <attribute name="type" ann:defaultValue="string">

                <choice>

                  <value>string</value>

                  <value>number</value>

                  <value>version</value>

                </choice>

              </attribute>

            </optional>

          </element>

          <element name="date_expression">

            <attribute name="id"><data type="ID"/></attribute>

            <choice>

              <group>

                <attribute name="operation"><value>in_range</value></attribute>

                <choice>

                  <group>

                    <optional>

                      <attribute name="start"><text/></attribute>

                    </optional>

                    <attribute name="end"><text/></attribute>

                  </group>

                  <group>

                    <attribute name="start"><text/></attribute>

                    <element name="duration">

                      <ref name="date-common"/>

                    </element>

                  </group>

                </choice>

              </group>

              <group>

                <attribute name="operation"><value>gt</value></attribute>

                <attribute name="start"><text/></attribute>

              </group>

              <group>

                <attribute name="operation"><value>lt</value></attribute>

                <choice>

                  <attribute name="end"><text/></attribute>

                </choice>

              </group>

              <group>

                <attribute name="operation"><value>date_spec</value></attribute>

                <element name="date_spec">

                  <ref name="date-common"/>

                </element> 

              </group>

            </choice>

          </element> 

          <ref name="element-rule"/>

        </choice>

      </oneOrMore>

     </group>

     </choice>

    </element>

  </define>

  <define name="date-common">

    <attribute name="id"><data type="ID"/></attribute>

    <optional>

      <attribute name="hours"><text/></attribute>

    </optional>

    <optional>

      <attribute name="monthdays"><text/></attribute>

    </optional>

    <optional>

      <attribute name="weekdays"><text/></attribute>

    </optional>

    <optional>

      <attribute name="yearsdays"><text/></attribute>

    </optional>

    <optional>

      <attribute name="months"><text/></attribute>

    </optional>

    <optional>

      <attribute name="weeks"><text/></attribute>

    </optional>

    <optional>

      <attribute name="years"><text/></attribute>

    </optional>

    <optional>

      <attribute name="weekyears"><text/></attribute>

    </optional>

    <optional>

      <attribute name="moon"><text/></attribute>

    </optional>

  </define>

</grammar>