Xsd 2个元素中的元素引用

我不知道我的问题怎么命名

我有一个XSD，它包含以下元素

 <xs:element name="abc">
   <xs:complexType>
     <xs:element maxOccurs="unbounded" ref="ele1"/>
   </xs:complexType>
 </xs:element>

 <xs:element name="xyz">
   <xs:complexType>
     <xs:element maxOccurs="unbounded" ref="ele1"/>
   </xs:complexType>
 </xs:element>

 <xs:element name="ele1">
   <xs:complexType>
     <xs:attribute name="ID" type="xs:integer"/>
   </xs:complexType>
 </xs:element>

---

问题是对于元素xyz ID是强制性的，而对于abc则不是；如何在XSD中指定此项？

假设ID是容器下重复内容的唯一标识符，则可以为xyz设置xs:key约束，如下所示：

<?xml version="1.0" encoding="utf-8" ?>
<xs:schema elementFormDefault="qualified" xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:element name="abc">
        <xs:complexType>
            <xs:sequence>
                <xs:element maxOccurs="unbounded" ref="ele1"/>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
    <xs:element name="xyz">
        <xs:complexType>
            <xs:sequence>
                <xs:element maxOccurs="unbounded" ref="ele1"/>
            </xs:sequence>
        </xs:complexType>
        <xs:key name="PK_xyz">
            <xs:selector xpath="ele1"/>
            <xs:field xpath="@ID"/>
        </xs:key>
    </xs:element>
    <xs:element name="ele1">
        <xs:complexType>
            <xs:attribute name="ID" type="xs:integer"/>
        </xs:complexType>
    </xs:element>
</xs:schema>

无效，因为它是重复的。如果上述关于唯一性的假设不成立，这就是缺点：

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<!-- Sample XML generated by QTAssistant (http://www.paschidev.com) -->
<xyz xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <ele1 ID="1"/>
    <ele1 ID="1"/>
</xyz>

工作样本：

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<!-- Sample XML generated by QTAssistant (http://www.paschidev.com) -->
<xyz xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <ele1 ID="1"/>
    <ele1 ID="2"/>
</xyz>

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<!-- Sample XML generated by QTAssistant (http://www.paschidev.com) -->
<xyz xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <ele1 ID="1"/>
    <ele1 ID="1"/>
</xyz>

Error occurred while loading [], line 5 position 3
There is a duplicate key sequence '1' for the 'PK_xyz' key or unique identity constraint.
Document3.xml is invalid.

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<!-- Sample XML generated by QTAssistant (http://www.paschidev.com) -->
<xyz xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <ele1 ID="1"/>
    <ele1 ID="2"/>
</xyz>