<!ATTLIST 元素名称 属性名称 数据类型 附加条件>

TIP：声明元素的时候，元素的数据类型是PCDATA

属性的时候，实行的数据类型是CDATA

dtd的代码：

<?xml version="1.0" encoding="UTF-8"?>
<!ELEMENT movies (movie+)>
<!ELEMENT movie (title,actor,rating)>
<!ELEMENT title (#PCDATA)>
<!ELEMENT actor (#PCDATA)>
<!ELEMENT rating (#PCDATA)>

<!ATTLIST movie id CDATA #required>
<!ATTLIST movie type CDATA #IMPLIED> 

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE movies SYSTEM "demo9.dtd">
<movies>
	<movie id="1" type="">
		<title/>
		<actor/>
		<rating/>
	</movie>
	<movie id="1">
		<title/>
		<actor/>
		<rating/>
	</movie>
</movies>

例题：写出下面xml的dtd文件

dtd代码：

<?xml version="1.0" encoding="UTF-8"?>
<!ELEMENT books (book+)>
<!ELEMENT book (#PCDATA)>
<!ATTLIST book id ID #required>
<!ATTLIST book medium CDATA #FIXED '纸质'>
<!ATTLIST book type CDATA '计算机'>
<!ATTLIST book pub (北京大学出版社|工业出版社|邮电出版社) "北京大学出版社">
<!ATTLIST book pagesize CDATA #IMPLIED>

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE books SYSTEM "demo10.dtd">
<books>
	<book id="s001" medium="纸质" type="计算机" pub="北京大学出版社" pagesize="300">
	</book>
</books>