带有可选子元素的默认 XML 序列(或全部)必须至少有一个子元素吗?

问题描述

如果有人能确认以下模式的解释是否正确，我将不胜感激:

I would be grateful if someone could confirm if the interpretation of the following schema is correct:

<xs:element name="Element1">
    <xs:complexType>
        <xs:sequence>
            <xs:element name="Child1" minOccurs="0" />
            <xs:element name="Child2" minOccurs="0" /> 
        </xs:sequence>
    </xs:complexType>
</xs:element>

虽然Child1 和Child2 都是可选的，但Element1 必须至少有一个子节点才能符合上述模式；即文档:

Although both Child1 and Child2 are optional, Element1 has to have at least one child to comply with the above schema; i.e. the document:

<Element1></Element1>    

不会遵守.为了使其有效，它需要序列 minOccurs = 0(?)

Would not comply. For this to be valid, it would require sequence minOccurs = 0(?)

更新

当子元素是可选的时，问题涉及序列(和所有)出现的含义.例如文档；

The question relates to the meaning of occurrence for sequence (and all) when child elements are optional. For example, the document;

<Element1>
    <Child2/>
    <Child1/>
</Element1>

将符合上述架构.该序列将发生两次；在第一遍中，Child1 缺席.在第二个中，Child2 缺席.但关键是，序列 minOccurs(默认为 1)是满足的，因为它发生了两次.

Would comply with the above schema. The sequence would have occurred twice; in the first pass, Child1 was absent. In the second, Child2 was absent. But the point is, the sequence minOccurs (default of 1) was satisfied, because it occurred twice.

对于我上面给出的第一个例子(只有 Element1；没有子元素)，序列根本不会出现，并且不 (IMO) 满足 minOccurs = 1.

With the first example I gave above (just Element1; no child elements), sequence does not occur at all, and does not (IMO) satisfy minOccurs = 1.

推荐答案

没有...

虽然 Child1 和 Child2 都是可选的，Element1 必须在至少有一个孩子符合上述模式

minOccurs 的默认值为 1，因此您可以正确地假设 xsd:sequence 被限制为出现一次.但是，只要满足其子项的出现约束一次，就满足 xsd:sequence minOccurs="1".当所有子出现约束为 minOccurs="0" 时，允许一个空序列.因此，即使没有任何 Child1 或 Child2 子元素， 也是有效的.

The default value for minOccurs is 1, so you're correct to assume that the xsd:sequence is constrained to appear once. However, xsd:sequence minOccurs="1" is satisfied as long as its children's occurrence constraints are satisfied once. When all child occurrence constraints are minOccurs="0", one empty sequence is allowed. Therefore, <Element1/> is valid, even without any Child1 or Child2 children elements.

另见

• XML Schema minOccurs/maxOccurs 默认值
• <all>的区别<序列>和<组>在 XSD 中?

带有 xs:sequence minOccurs="0"

<xs:element name="r">
    <xs:complexType>
        <xs:sequence minOccurs="0" maxOccurs="1">
            <xs:element name="a"/>
            <xs:element name="b"/> 
        </xs:sequence>
    </xs:complexType>
</xs:element>

有效的 XML: ;

Valid XML: <r/> and <r><a/><b/></r>

带有 xs:sequence minOccurs="1" 的 XSD(默认)

XSD with xs:sequence minOccurs="1" (default)

<xs:element name="r">
    <xs:complexType>
        <xs:sequence minOccurs="1" maxOccurs="1">
            <xs:element name="a"/>
            <xs:element name="b"/> 
        </xs:sequence>
    </xs:complexType>
</xs:element>

有效的 XML: <r><a/><b/></r>

带有 xs:sequence minOccurs="2"

<xs:element name="r">
    <xs:complexType>
        <xs:sequence minOccurs="2" maxOccurs="2">
            <xs:element name="a"/>
            <xs:element name="b"/> 
        </xs:sequence>
    </xs:complexType>
</xs:element>

有效的 XML: <r><a/><b/><a/><b/></r>

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