XML and DTD的简单定义

xml：xml是可扩展的标记性语言，它主要是用来存储数据，被喻为：小型数据库
它不存在预定义标记，全部都是要自定义的标记
优点：准确性高 
说html和xml的区别：
xml:就是用来传送和存储数据
html：就会显示数据
在同一个文件中

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE school [
	<!ELEMENT school (grade?,weclome*,filter+)>
	<!ELEMENT grade (class)>
	<!ELEMENT class (student+)>
	<!ELEMENT student (#PCDATA)>
	<!ATTLIST school name CDATA #FIXED "可爱的学校"
					address CDATA #IMPLIED
	>
	<!ATTLIST student no ID #IMPLIED
			sex (男|女) "女"
			name CDATA #REQUIRED
	>
	<!ENTITY SCHOOLNAME "可爱的学校">
]>
<school name="可爱的学校">
	<grade>
		<class>
			<student no="A1000" sex="男" name="&quot;可爱的学校&quot;">&SCHOOLNAME;</student>
			<student no="A1001" sex="女? name="乖乖"></student>
		</class>
	</grade>
	<filter>
	</filter>
</school>

不在同一个文件
DTD文件中

<?xml version="1.0" encoding="UTF-8"?>

<!ELEMENT webapp (global,package+)>
<!ELEMENT global (result)>
<!ELEMENT package (action+)>
<!ELEMENT action (result)>
<!ELEMENT result (#PCDATA)>

<!ATTLIST package name CDATA #REQUIRED
				  namespace CDATA #REQUIRED		  
>
<!ATTLIST action name CDATA #REQUIRED
				 type CDATA #REQUIRED
				 method CDATA #REQUIRED		  
>
<!ATTLIST result name CDATA #REQUIRED
				 path CDATA #REQUIRED	
				 redirect (true|false) "false"
>

xml文件中

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE webapp SYSTEM "action.dtd">
<webapp>
	<global>
		<result name="error" path="error.jsp" redirect="true"></result>
	</global>
	<package name="student" namespace="/student">
		<action name="StudentAction" type="com.lxit.ext.student.action" method="getStudent">
			<result name="success" path="success.jsp"></result>
		</action>
		<action name="StudentAction" type="com.lxit.ext.student.action" method="update">
			<result name="success" path="success.jsp"></result>
		</action>
	</package>
	<package name="classes" namespace="/classes">
		<action name="ClassesAction" type="com.lxit.ext.classes.action" method="getClasses">
			<result name="success" path="success.jsp"></result>
		</action>
		<action name="ClassesAction" type="com.lxit.ext.classes.action" method="update">
			<result name="success" path="success.jsp"></result>
		</action>
	</package>
</webapp>