有約束效果但是在teaching-plan上面爆紅

xsd的：

<?xml version="1.0" encoding="UTF-8"?>

<schema xmlns="http://www.w3.org/2001/XMLSchema">

<element name="teaching-plan">

<complexType>

<sequence >

<element name="course" minOccurs="1" maxOccurs="100">

<complexType>

<sequence>

<element name="course-name" type="string"></element>

<element name="class-hour">

<simpleType>

<restriction base="integer">

<minExclusive value="20"></minExclusive>

<maxExclusive value="110"></maxExclusive>

</restriction>

</simpleType>

</element>

<element name="exam-form" type="string"></element>

</sequence>

</complexType>

</element>

</sequence>

<attribute name="id" type="string" use="required"></attribute>

</complexType>

</element>

</schema> 

xml的：

<?xml version="1.0" encoding="UTF-8"?>

<teaching-plan xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="hr.xsd">

<course>

<course-name>大学英语</course-name>

<class-hour>30</class-hour>

<exam-form>考试</exam-form>

</course>

<course>

<course-name>高等数学</course-name>

<class-hour>70</class-hour>

<exam-form>考试</exam-form>

</course>

<course>

<course-name>计算机应用基础</course-name>

<class-hour>100</class-hour>

<exam-form>上机考试</exam-form>

</course>

</teaching-plan>

有約束效果但是在teaching-plan上面爆紅 報錯是cvc-complex-type.4: Attribute 'id' must appear on element 'teaching-plan'. ？ 翻譯是：

cvc complex type.4:属性'id'必须出现在元素'teaching plan'上。

？這個是什麽原因啊老師