XML 模式，为什么 xs:group 不能是 xs:all 的孩子? [英] XML schema, why xs:group can't be child of xs:all?

问题描述

根据此页面 (和我的实践)，xs:group 元素不能是 xs:all 的子元素.所以像

According to this page (and my practice), xs:group element cannot be child of xs:all. So something like

<xs:group name="g">
    <xs:element name="first" type="xs:string"/>
    <xs:element name="last" type="xs:string"/>
</xs:group>
<xs:all>
    <xs:group ref="g" minOccurs="0" maxOccurs="1"/>
    <xs:element name="id" type="xs:string"/>
</xs:all>

无效，因为组不能在 xs:all 内.但是我想定义一个模式，其中两个元素(上面示例中的 first 和 last )都存在或都不存在，所以我将它们组合成一个组.然后我想让 xs:all 成为组的一部分，因为该组可以以任何顺序与其他元素(例如上面的 id 元素)一起出现.换句话说，我希望有几个元素作为一个整体是可选的.如果 xs:group 不能成为 xs:all 的孩子，我该如何实现?

is not valid because group cannot be inside xs:all. But I want to define a schema, in which two elements (first and last in above example) both exist or neither of them exists, so I make them into a group. Then I want to make the group part of xs:all because the group can appear with other elements (for example, id element above) in any order. In other words, I want to have several elements are optional as a whole group. Without xs:group being able to be child of xs:all, how can I achieve this?

推荐答案

XMLSchema 1.0 只允许在 xs:all 下使用 xs:element(和 xs:annotation).

<all
  id = ID
  maxOccurs = 1 : 1
  minOccurs = (0 | 1) : 1
  {any attributes with non-schema namespace . . .}>
  Content: (annotation?, element*)
</all>

它不允许 xs:group、xs:sequence、xs:choice 等

XML Schema 1.1 许可 xs:element<xs:all:

<all
  id = ID
  maxOccurs = (0 | 1) : 1
  minOccurs = (0 | 1) : 1
  {any attributes with non-schema namespace . . .}>
  Content: (annotation?, (element | any | group)*)
</all>

注意:允许无序元素听起来很理想，但很少真正需要.通常 xs:sequence 在实践中就足够了.

Note: Allowing unordered elements may sound ideal but rarely is truly needed. Usually xs:sequence suffices in practice.

如果您愿意放弃无序要求，您可以(即使在 XSD 1.0 中)要求 first 和 last都存在或都不存在"作为如下:

If you are willing to forgo the unordered requirement, you could (even in XSD 1.0) require first and last to "both exist or neither of them exist" as follows:

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

  <xs:element name="a">
    <xs:complexType>
      <xs:sequence>
        <xs:sequence minOccurs="0">
          <xs:element name="first" type="xs:string"/>
          <xs:element name="last" type="xs:string"/>
        </xs:sequence>
        <xs:element name="id" type="xs:string"/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

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