XML 和 XML-Schema 基数问题

Question

我有 XML 和 XML 架构。 XML 包含过滤器，并且可以在另一个过滤器中包含过滤器。现在我尝试在架构中使用 key 和 keyref 但收到错误

The cardinality of the fields in keyref 'FilterKeyRef' must be equal to the cardinality of the identity constraint definition 'FilterIdKey'. The cardinality must be '1'

。我尝试使用多种在线工具、人工智能以及同事，但仍然无法解决该错误。有人知道如何解决这个问题吗？

这是 XML：

<?xml version="1.0" encoding="UTF-8"?>
<Filters xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="example.xsd">
    <Filter>
        <Id>0</Id>
        <DisplayName>Filter1</DisplayName>
    </Filter>
    <Filter>
        <Id>1</Id>
        <DisplayName>Filter2</DisplayName>
    </Filter>
    <Filter>
        <Id>2</Id>
        <DisplayName>Filter3</DisplayName>
        <FiltersToInclude>
            <FilterToInclude>
                <Id>0</Id>
                <DisplayName>Filter1</DisplayName>
            </FilterToInclude>
            <FilterToInclude>
                <Id>1</Id>
                <DisplayName>Filter2</DisplayName>
            </FilterToInclude>
        </FiltersToInclude>
    </Filter>
</Filters>

这是 XML 架构：

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

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

        <xs:element name="DisplayName" type="xs:string"/>
        <xs:element name="Id" type="xs:nonNegativeInteger"/>    
        
        <xs:element name="Filter">
            <xs:complexType>
                <xs:sequence>
                    <xs:element ref="Id" minOccurs="1" maxOccurs="1"/>
                    <xs:element ref="DisplayName" minOccurs="1" maxOccurs="1"/>
                    <xs:element ref="FiltersToInclude" minOccurs="0" maxOccurs="unbounded"/>
                </xs:sequence>
            </xs:complexType>
        </xs:element>
        
        <xs:element name="FilterToInclude">
            <xs:complexType>
                <xs:sequence>
                    <xs:element ref="Id" minOccurs="1" maxOccurs="1"/>
                    <xs:element ref="DisplayName" minOccurs="1" maxOccurs="1"/>
                </xs:sequence>
            </xs:complexType>
        </xs:element>
        
        <xs:element name="FiltersToInclude">
            <xs:complexType>
                <xs:sequence>
                    <xs:element ref="FilterToInclude" minOccurs="1" maxOccurs="unbounded"/>
                </xs:sequence>
            </xs:complexType>
        </xs:element>       
        
        <xs:element name="Filters">
            <xs:complexType>
                <xs:sequence>
                    <xs:element ref="Filter" minOccurs="1" maxOccurs="unbounded"/>
                </xs:sequence>
            </xs:complexType>
            <xs:key name="FilterIdKey">
                <xs:selector xpath="Filter/Id"></xs:selector>
                <xs:field xpath="."></xs:field>
            </xs:key>
            <xs:key name="FilterDisplayNameKey">
                <xs:selector xpath="Filter/DisplayName"></xs:selector>
                <xs:field xpath="."></xs:field>
            </xs:key>
            <xs:keyref name="FilterKeyRef" refer="FilterIdKey">
                <xs:selector xpath="Filter/FiltersToInclude/FilterToInclude"></xs:selector>
                <xs:field xpath="./Id"></xs:field>
                <xs:field xpath="./DisplayName"></xs:field>
            </xs:keyref>
        </xs:element>
</xs:schema>

Answer 1

感谢 Martin Honnen 的评论，我成功做到了。

这是新的 XML 架构：

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

<!-- W3C Schema generated by XMLSpy v2021 rel. 3 (x64) (http://www.altova.com) -->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

        <!--     simple elements -->
        <xs:element name="DisplayName" type="xs:string"/>
        <xs:element name="Id" type="xs:nonNegativeInteger"/>    
        
        <xs:element name="Filter">
            <xs:complexType>
                <xs:sequence>
                    <xs:element ref="Id" minOccurs="1" maxOccurs="1"/>
                    <xs:element ref="DisplayName" minOccurs="1" maxOccurs="1"/>
                    <xs:element ref="FiltersToInclude" minOccurs="0" maxOccurs="unbounded"/>
                </xs:sequence>
            </xs:complexType>
        </xs:element>
        
        <xs:element name="FilterToInclude">
            <xs:complexType>
                <xs:sequence>
                    <xs:element ref="Id" minOccurs="1" maxOccurs="1"/>
                    <xs:element ref="DisplayName" minOccurs="1" maxOccurs="1"/>
                </xs:sequence>
            </xs:complexType>
        </xs:element>
        
        <xs:element name="FiltersToInclude">
            <xs:complexType>
                <xs:sequence>
                    <xs:element ref="FilterToInclude" minOccurs="1" maxOccurs="unbounded"/>
                </xs:sequence>
            </xs:complexType>
        </xs:element>       
        
        <xs:element name="Filters">
            <xs:complexType>
                <xs:sequence>
                    <xs:element ref="Filter" minOccurs="1" maxOccurs="unbounded"/>
                </xs:sequence>
            </xs:complexType>
            <xs:key name="FilterKey">
                <xs:selector xpath="Filter"></xs:selector>
                <xs:field xpath="Id"></xs:field>
                <xs:field xpath="DisplayName"></xs:field>
            </xs:key>
            <xs:keyref name="FilterKeyRef" refer="FilterKey">
                <xs:selector xpath="Filter/FiltersToInclude/FilterToInclude"></xs:selector>
                <xs:field xpath="./Id"></xs:field>
                <xs:field xpath="./DisplayName"></xs:field>
            </xs:keyref>
        </xs:element>
</xs:schema>