输入了attribute也报错

<?xml version="1.0" encoding="UTF-8"?> <!-- 用来定义属性 required必须的 use就是在no在employee必须存在 -->
<schema xmlns="http://www.w3.org/2001/XMLSchema" >
<element name="hr">
   <!-- complexType标签含义是复杂节点，包含子节点时必须使用这个标签 -->
   <complexType>
        <!-- sequence序列的意思 -->
       <sequence>
            <element name="employee">
                <complexType>
                   <sequence>
                      <element name="course-name" type="string"></element>
                      <element name="class-hour" type="integer"></element>
                      <element name="exam-form" type="string"  > </element>                
                   </sequence>
                </complexType>
            </element>
       </sequence>
       <attribute name="no" type="string" use="optional"> </attribute>
   </complexType>
</element>
</schema>

<?xml version="1.0" encoding="UTF-8"?>
<!--  日历资源 -->
<hr xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  xsi:noNamespaceSchemaLocation="hr.xsd">
 <employee no = "01">
  <course-name>大学英语</course-name>
  <class-hour>36</class-hour> 
  <exam-form>考试</exam-form>
 </employee>
 <employee no = "02">
  <course-name>高等数学</course-name>
  <class-hour>70</class-hour> 
  <exam-form>考试</exam-form>
 </employee>
 <employee no = "03">
  <course-name>计算机应用基础</course-name>
  <class-hour>108</class-hour> 
  <exam-form>上机考试</exam-form>
 </employee>
</hr>