DTD-ID属性的唯一性 [英] DTD - uniqueness of ID attributes

问题描述

根据关于ID属性类型的DTD规范：

有效性约束：ID

Validity constraint: ID

ID类型的值必须与Name产生的值匹配。名称
不能在XML文档中多次出现。
，即ID值必须唯一地标识承载它们的元素。

Values of type ID MUST match the Name production. A name MUST NOT appear more than once in an XML document as a value of this type; i.e., ID values MUST uniquely identify the elements which bear them.

以下哪种解释正确？

Which of the following explanations is correct?

1. 类型ID的所有属性的所有实例的值必须不同。


2. 所有实例的值必须不同

换句话说，给定以下DTD声明代码段：

In other words, given the following DTD declaration snippet:

<!ELEMENT book ANY>
<!ATTLIST book id ID>

<!ELEMENT magazine ANY>
<!ATTLIST magazine id ID>

以下XML文档摘要是否违反了有效性约束？

does the following XML document snippet violate the validity constraint?

<book id="ID01" />
<magazine id="ID01" />

如何将属性重命名为 book-id 和 magazine-id ，而不是在两种情况下都只是 id ？

How about if I renamed the attributes to book-id and magazine-id, instead of just id in both cases?

推荐答案

案例1

格式良好的XML文档：

Case 1

Well-formed XML document:

<!DOCTYPE root SYSTEM "idtest.dtd">
<root>
  <book id="ID01" />
  <magazine id="ID01" />
</root>

DTD：

<!ELEMENT root ANY>

<!ELEMENT book ANY>
<!ATTLIST book id ID #IMPLIED>

<!ELEMENT magazine ANY>
<!ATTLIST magazine id ID #IMPLIED>

xmllint的输出：

Output from xmllint:

$ xmllint --postvalid idtest.xml
<?xml version="1.0"?>
<!DOCTYPE root SYSTEM "idtest.dtd">
<root>
  <book id="ID01"/>
  <magazine id="ID01"/>
</root>
idtest.xml:4: element magazine: validity error : ID ID01 already defined
  <magazine id="ID01" />
                      ^
idtest.xml:4: element magazine: validity error : ID ID01 already defined
Document idtest.xml does not validate

案例2

格式良好的XML文档：

Case 2

Well-formed XML document:

<!DOCTYPE root SYSTEM "idtest.dtd">
<root>
  <book book_id="ID01" />
  <magazine magazine_id="ID01" />
</root>

DTD：

<!ELEMENT root ANY>

<!ELEMENT book ANY>
<!ATTLIST book book_id ID #IMPLIED>

<!ELEMENT magazine ANY>
<!ATTLIST magazine magazine_id ID #IMPLIED>

xmllint的输出：

Output from xmllint:

$ xmllint --postvalid idtest.xml
<?xml version="1.0"?>
<!DOCTYPE root SYSTEM "idtest.dtd">
<root>
  <book book_id="ID01"/>
  <magazine magazine_id="ID01"/>
</root>
idtest.xml:4: element magazine: validity error : ID ID01 already defined
  <magazine magazine_id="ID01" />
                               ^
idtest.xml:4: element magazine: validity error : ID ID01 already defined
Document idtest.xml does not validate

结论：更改属性名称没有帮助。类型很重要。 ID类型的属性值必须唯一。解释1是正确的。

Conclusion: Changing the attribute names does not help. The type is what matters. Values of attributes of type ID must be unique. Explanation 1 is correct.

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