定义了xml和dtd文件,但是dtd的属性约束没有效果。
xml 文件
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE books SYSTEM "books2.dtd">
<books>
<book id="a123" city="阿斯顿">
<name>
</name>
<author>
</author>
<price>
123
</price>
</book>
<book id="a123">
<name>
</name>
<author>
</author>
<price>
321
</price>
</book>
</books>
下面是dtd文件
<?xml version="1.0" encoding="UTF-8"?>
<!ELEMENT books (book+)>
<!ELEMENT book (name?,author,(price|money))>
<!ELEMENT name (#PCDATA)>
<!ELEMENT author (#PCDATA)>
<!ELEMENT price (#PCDATA)>
<!ATTLIST book
id ID #REQUIRED
title CDATA #IMPLIED
lang CDATA #FIXED "固定值"
category CDATA "默认值"
pId IDREF #REQUIRED
city (北京|上海|广州) #REQUIRED
>