如何在XSD中定义元素OR逻辑？无法修改旧结构

• 无法修改“OLD STYLE BLOCK”结构，只能扩展现有XML结构
• 尝试编写的XSD出现解析错误，原本希望在xs:complexType中同时使用xsd:choice和xs:sequence
• 能否通过Version="2.0"为XSD添加额外逻辑？

示例XML #

<?xml version="1.0"?>
<MyStruct Version="2.0">

   <!-- xs should allow "NEW STYLE BLOCK" OR "OLD STYLE BLOCK" with array of id -->
   <!-- one of them should present !!!! -->

  <!-- NEW STYLE BLOCK my complex type-->
  <IDArray>
    <IDSet>
        <ID>89</ID>
        <ID>1</ID>
        <ID>2</ID>
    </IDSet>
    <IDSet>
        <ID>3</ID>
        <ID>4</ID>
    </IDSet>
  </IDArray>
  <!-- end of NEW STYLE BLOCK -->

  <!-- OLD STYLE BLOCK  array of elements  -->
  <ID>5</ID>
  <ID>7</ID>
  <!-- end of OLD STYLE BLOCK -->

  <Type>Some type</Type>  <!-- mandatory element -->
  <ReadableName>Human readable name</ReadableName>  <!-- mandatory element -->
</MyStruct>

拟议的XSD #

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" version="1.1">

  <xs:element name="MyStruct">
    <xs:complexType>

        <xs:choice>
            <xs:element name="IDArray" minOccurs="0" maxOccurs="1">
                <xs:complexType>
                      <xs:choice maxOccurs="unbounded">
                        <xs:element name="IDSet" minOccurs="1" maxOccurs="unbounded">
                            <xs:complexType>
                                  <xs:choice maxOccurs="unbounded">
                                      <xs:element name="ID" minOccurs="1" maxOccurs="unbounded" />
                                  </xs:choice>
                            </xs:complexType>
                        </xs:element>
                      </xs:choice>
                </xs:complexType>
            </xs:element>

            <xs:element name="ID" minOccurs="0" maxOccurs="unbounded" />
        </xs:choice>

        <xs:sequence>
            <xs:element name="Type" type="xs:string" />
            <xs:element name="ReadableName" type="xs:string" />
        </xs:sequence>  <!--  error in this line  -->

      <xs:attribute name="Version" type="xs:string" />

    </xs:complexType>
  </xs:element>
</xs:schema>

错误信息 #

./MyStruct.xsd:: element sequence: Schemas parser error : Element '{http://www.w3.org/2001/XMLSchema}complexType': The content is not valid. Expected is (annotation?, (simpleContent | complexContent | ((group | all | choice | sequence)?, ((attribute | attributeGroup)*, anyAttribute?)))).

问题分析与解决方案 #

1. 解析错误原因 #

XSD的xs:complexType内容模型规则明确：顶层只能包含一个内容模型容器（choice/sequence/all/group等），不能直接并列choice和sequence，你的写法违反了这个规则，因此报错。

2. 正确实现OR逻辑的XSD #

要实现「IDArray（新结构）OR 多个ID（旧结构）二选一，同时必须包含Type和ReadableName」的需求，需要把choice和sequence包裹在一个外层sequence中，并给choice设置minOccurs="1"确保二选一：

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" version="1.1">

  <xs:element name="MyStruct">
    <xs:complexType>
      <!-- 外层sequence：先选IDArray或多个ID，再必须出现Type和ReadableName -->
      <xs:sequence>
        <!-- choice设置minOccurs="1"，确保二选一 -->
        <xs:choice minOccurs="1" maxOccurs="1">
          <xs:element name="IDArray">
            <xs:complexType>
              <!-- IDSet为有序重复，用sequence更合理 -->
              <xs:sequence maxOccurs="unbounded">
                <xs:element name="IDSet">
                  <xs:complexType>
                    <!-- ID为有序重复，用sequence -->
                    <xs:sequence maxOccurs="unbounded">
                      <xs:element name="ID" type="xs:string" />
                    </xs:sequence>
                  </xs:complexType>
                </xs:element>
              </xs:sequence>
            </xs:complexType>
          </xs:element>

          <xs:element name="ID" type="xs:string" minOccurs="1" maxOccurs="unbounded" />
        </xs:choice>

        <!-- 必须出现的Type和ReadableName -->
        <xs:sequence>
          <xs:element name="Type" type="xs:string" />
          <xs:element name="ReadableName" type="xs:string" />
        </xs:sequence>
      </xs:sequence>

      <xs:attribute name="Version" type="xs:string" />
    </xs:complexType>
  </xs:element>
</xs:schema>

3. 利用Version属性添加额外逻辑（XSD 1.1特性） #

如果需要根据Version属性区分允许的结构（比如仅Version="2.0"允许新结构，旧版本只能用旧结构），可以使用XSD 1.1的xs:assert断言：

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" version="1.1">

  <xs:element name="MyStruct">
    <xs:complexType>
      <xs:sequence>
        <xs:choice minOccurs="0" maxOccurs="1">
          <xs:element name="IDArray">
            <xs:complexType>
              <xs:sequence maxOccurs="unbounded">
                <xs:element name="IDSet">
                  <xs:complexType>
                    <xs:sequence maxOccurs="unbounded">
                      <xs:element name="ID" type="xs:string" />
                    </xs:sequence>
                  </xs:complexType>
                </xs:element>
              </xs:sequence>
            </xs:complexType>
          </xs:element>
        </xs:choice>

        <xs:element name="ID" type="xs:string" minOccurs="0" maxOccurs="unbounded" />

        <xs:sequence>
          <xs:element name="Type" type="xs:string" />
          <xs:element name="ReadableName" type="xs:string" />
        </xs:sequence>
      </xs:sequence>

      <xs:attribute name="Version" type="xs:string" use="required" />

      <!-- 断言逻辑：Version="2.0"时可选IDArray或ID；旧版本只能用ID -->
      <xs:assert test="(Version='2.0' and (IDArray or ID)) or (Version!='2.0' and ID and not(IDArray))"/>
      <!-- 确保至少有一个ID相关结构 -->
      <xs:assert test="IDArray or ID"/>
    </xs:complexType>
  </xs:element>
</xs:schema>

注意：XSD 1.1需要支持该版本的解析器（如Apache Xerces2 2.12+、Saxon等）。

内容的提问来源于stack exchange，提问作者Vlad