Schema问题，急！急！急！

Question

<?xml version="1.0" encoding="UTF-8"?>
<!--W3C Schema generated by XMLSPY v2004 rel. 3 U (http://www.xmlspy.com)-->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified">
     <xs:element name="CDCA-WFS-WORK-CALENDAR">
          <xs:complexType>
               <xs:sequence>
                    <xs:element name="MONTH-FREE-DAYS" ref="MONTH-FREE-DAYS"/>
                    <xs:element name="SPECIAL-WORKHOURS-DAYS" ref="SPECIAL-WORKHOURS-DAYS"/>
               </xs:sequence>
               <xs:attribute name="YEAR" type="xs:short" use="required"/>
               <xs:attribute name="WORKHOURSPERDAY" type="xs:byte" use="required"/>
          </xs:complexType>
     </xs:element>
     <xs:element name="DAY">
          <xs:complexType>
               <xs:attribute name="MONTH" type="xs:byte" use="required"/>
               <xs:attribute name="DAY" type="xs:byte" use="required"/>
               <xs:attribute name="WORKHOURS" type="xs:byte" use="required"/>
          </xs:complexType>
     </xs:element>
     <xs:element name="Feb">
          <xs:complexType/>
     </xs:element>
     <xs:element name="Jan" type="xs:string"/>
     <xs:element name="MONTH-FREE-DAYS">
          <xs:complexType>
               <xs:sequence>
                    <xs:element name="Jan" ref="Jan"/>
                    <xs:element name="Feb" ref="Feb"/>
                    <xs:element name="Oct" ref="Oct"/>
                    <xs:element name="Nov" ref="Nov"/>
               </xs:sequence>
          </xs:complexType>
     </xs:element>
     <xs:element name="Nov">
          <xs:complexType/>
     </xs:element>
     <xs:element name="Oct" type="xs:string"/>
     <xs:element name="SPECIAL-WORKHOURS-DAYS">
          <xs:complexType>
               <xs:sequence>
                    <xs:element name="DAY" ref="DAY"/>
               </xs:sequence>
          </xs:complexType>
     </xs:element>
</xs:schema>