如何在 XML 模式中实现互斥属性？

发布于 2024-07-10 12:54:25 字数 235 浏览 11 评论 0原文

我试图使两个 XML 属性互斥。如何创建 XSD 模式来捕获这种场景？

我想要其中之一

<elem value="1" />
<elem ref="something else" />

，但没有

<elem value="1" ref="something else" />

原文

I'm trying to make two XML attributes to be mutually exclusive. How can one create an XSD schema to capture this kind of scenario?

I would like to have one of these

<elem value="1" />
<elem ref="something else" />

but not

<elem value="1" ref="something else" />

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说谎友 2024-07-17 12:54:25

您不能使用属性，但可以使用子元素...

<element name="elem">
    <complexType>
        <choice>
            <element name="value"/>
            <element name="ref"/>
        </choice>
    </complexType>
</element>

这样您就可以拥有...

<elem>
    <value>1</value>
</elem>

或...

<elem>
    <rel>something else</rel>
</elem>

You can't do with attributes, but you can with child elements...

<element name="elem">
    <complexType>
        <choice>
            <element name="value"/>
            <element name="ref"/>
        </choice>
    </complexType>
</element>

This way you can have...

<elem>
    <value>1</value>
</elem>

or...

<elem>
    <rel>something else</rel>
</elem>

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沉溺在你眼里的海 2024-07-17 12:54:25

不幸的是，据我所知，您无法使用 XML Schema 做到这一点，我自己也遇到了同样的问题。

我看到它建议，如果您需要两者：

<elem type="xxx"> 
<elem ref="yyy">

那么本身应该分为两种类型，因为它们显然具有不同的属性......

Unfortunately AFAIK you can't do that with XML Schema, I've had the same problem myself.

I've seen it suggested that if you need both of:

<elem type="xxx"> 
<elem ref="yyy">

then <elem> itself should be split into two types, since they've clearly got different attributes...

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指尖上得阳光 2024-07-17 12:54:25

由于 Alnitak 的回答中提到了 RelaxNG ，这里有一个解决方案
使用 RelaxNG（一种在大多数情况下比 W3C 更好的语言）
架构）。请注意 elem 定义中的 OR (|)：

start = document
document = element document {elem+}
elem = element elem {ref | value}
ref = attribute ref {text}
value = attribute value {xsd:integer}

如果我有此 XML 文件：

<document>
    <elem value="1" />
    <elem ref="something else" />
</document>

它被 rnv 接受和 xmlint：

 % rnv attributes-exclusive.rnc attributes-exclusive.xml             
 attributes-exclusive.xml

 % xmllint --noout --relaxng attributes-exclusive.rng attributes-exclusive.xml 
 attributes-exclusive.xml validates

如果我在 XML 文件中添加：

<elem value="1" ref="something else" />

我会收到验证错误，如我所愿（请注意错误信息
是次优的）：

% rnv attributes-exclusive.rnc attributes-exclusive.xml    
attributes-exclusive.xml
attributes-exclusive.xml:4:0: error: attribute ^ref not allowed
required:
       after

% xmllint --noout --relaxng attributes-exclusive.rng attributes-exclusive.xml
attributes-exclusive.xml:4: element elem: Relax-NG validity error : Invalid attribute value for element elem
attributes-exclusive.xml fails to validate

Since RelaxNG was mentioned in Alnitak's answer, here is a solution
with RelaxNG (a language which is, in most cases, better than W3C
Schema). Do note the OR (|) in the definition of elem:

start = document
document = element document {elem+}
elem = element elem {ref | value}
ref = attribute ref {text}
value = attribute value {xsd:integer}

If I have this XML file:

<document>
    <elem value="1" />
    <elem ref="something else" />
</document>

It is accepted by rnv and xmlint:

 % rnv attributes-exclusive.rnc attributes-exclusive.xml             
 attributes-exclusive.xml

 % xmllint --noout --relaxng attributes-exclusive.rng attributes-exclusive.xml 
 attributes-exclusive.xml validates

If I add in the XML file:

<elem value="1" ref="something else" />

I get validation errors, as I want (do note that the error messages
are suboptimal):

% rnv attributes-exclusive.rnc attributes-exclusive.xml    
attributes-exclusive.xml
attributes-exclusive.xml:4:0: error: attribute ^ref not allowed
required:
       after

% xmllint --noout --relaxng attributes-exclusive.rng attributes-exclusive.xml
attributes-exclusive.xml:4: element elem: Relax-NG validity error : Invalid attribute value for element elem
attributes-exclusive.xml fails to validate

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睡美人的小仙女 2024-07-17 12:54:25

实际上，可以通过 xs:unique 或 xs:key 使用身份约束在 XSD 1.0 中定义这一点。您选择哪一个取决于如何处理没有这两个属性之一的元素：它们对于 xs:unique 有效，但对于 xs:key 无效。下面的代码示例包含这两种变体；确保删除其中之一，否则“更严格”的 xs:key 优先于 xs:unique，即需要两个属性之一。

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           elementFormDefault="qualified" attributeFormDefault="unqualified">
  <xs:element name="container">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="elem" maxOccurs="unbounded">
          <xs:complexType>
            <xs:attribute name="value" use="optional"/>
            <xs:attribute name="ref" use="optional"/>
          </xs:complexType>
          <!-- Note: Use either xs:unique or xs:key -->
          <xs:unique name="attrsExclusiveOptional">
            <xs:annotation>
              <xs:documentation>Ensure that @value and @ref cannot occur simultaneously.
Both may be omitted.</xs:documentation>
            </xs:annotation>
            <xs:selector xpath="."/>
            <xs:field xpath="@value | @ref"/>
          </xs:unique>
          <xs:key name="attrsExclusiveRequired">
            <xs:annotation>
              <xs:documentation>Ensure that @value and @ref cannot occur simultaneously.
One of them is required.</xs:documentation>
            </xs:annotation>
            <xs:selector xpath="."/>
            <xs:field xpath="@value | @ref"/>
          </xs:key>
        </xs:element>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

这将验证以下 XML 文件：

<?xml version="1.0" encoding="UTF-8"?>
<container xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:noNamespaceSchemaLocation="schema.xsd">
  <!-- Shall pass: -->
  <elem value="1" />
  <elem ref="something else" />

  <!-- Passes for xs:unique, fails for xs:key: -->
  <elem />

  <!-- Shall fail: -->
  <elem value="1" ref="something else" />
</container>

Actually, it is possible to define this in XSD 1.0 using identity constraints via xs:unique or xs:key. Which one you choose depends on how elements without either of the two attributes shall be treated: They're valid with xs:unique but invalid with xs:key. The code sample below contains both variants; make sure to remove one of them, otherwise the "stricter" xs:key takes precedence over xs:unique, i.e., one of the two attributes is required.

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           elementFormDefault="qualified" attributeFormDefault="unqualified">
  <xs:element name="container">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="elem" maxOccurs="unbounded">
          <xs:complexType>
            <xs:attribute name="value" use="optional"/>
            <xs:attribute name="ref" use="optional"/>
          </xs:complexType>
          <!-- Note: Use either xs:unique or xs:key -->
          <xs:unique name="attrsExclusiveOptional">
            <xs:annotation>
              <xs:documentation>Ensure that @value and @ref cannot occur simultaneously.
Both may be omitted.</xs:documentation>
            </xs:annotation>
            <xs:selector xpath="."/>
            <xs:field xpath="@value | @ref"/>
          </xs:unique>
          <xs:key name="attrsExclusiveRequired">
            <xs:annotation>
              <xs:documentation>Ensure that @value and @ref cannot occur simultaneously.
One of them is required.</xs:documentation>
            </xs:annotation>
            <xs:selector xpath="."/>
            <xs:field xpath="@value | @ref"/>
          </xs:key>
        </xs:element>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

This validates the following XML file:

<?xml version="1.0" encoding="UTF-8"?>
<container xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:noNamespaceSchemaLocation="schema.xsd">
  <!-- Shall pass: -->
  <elem value="1" />
  <elem ref="something else" />

  <!-- Passes for xs:unique, fails for xs:key: -->
  <elem />

  <!-- Shall fail: -->
  <elem value="1" ref="something else" />
</container>

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