( )

Used to group elements

（古龙|Jin Yong|Liang Yusheng),(Wang Shuo|Yu Jie)

Divided into two groups

|

Select one of the listed objects

(Men|Women)

means that a man or a woman must appear, and you can only choose one

(1 or multiple times)

+）

to many times)

)

to 1 times)

）

Apple,banana） ## means watermelon, apple, banana must appear, and appear in this order

# #

Attributes

##Attribute name Type Attribute attribute

Attribute name Type Attribute characteristics......>

Explanation:

ATTLIST

Element name: The name of the corresponding element.

Attribute: There can be multiple attributes, and the format is name type attribute property

Type:

##PS

CDATA(Character type), enumeration (The enumeration format is (value1| Value2|Value3...)),ID(ID cannot be repeated and cannot start with a number ), IDREF( refers to another IDValue),IDREFS(can reference multiple ID Values, separated by spaces )

Attribute characteristics are:

Case:

<!ELEMENT 班级 (学生+,作者)>
<!ATTLIST 班级
	班次 CDATA "1班"
	编号 ID #REQUIRED
>
<!ELEMENT 学生 (名字,年龄,介绍)>
<!ELEMENT 作者 (#PCDATA)>
<!ATTLIST 学生
	地址 CDATA #IMPLIED
	授课方式 CDATA #FIXED "面授"
	学号 ID #REQUIRED
	班级编号 IDREF #REQUIRED
	朋友 IDREFS #IMPLIED
>
<!ELEMENT 名字 (#PCDATA)>
<!ELEMENT 年龄 (#PCDATA)>
<!ELEMENT 介绍 (#PCDATA)>

Entity

XML

, and parameter entities are generally used in DTD. Basic syntax

##Entity name

"Entity content"> // Reference entity##Entity name

"Entity content" > // Parameter entityExplanation: 1, the reference entity can be referenced

DTD

XML file, use &entity name; to use entity content. 2. I don’t know if it’s because of my computer. You can’t use reference entities in external DTD

. If you use it, put the reference entity definition in In the internal DTD, it can be used. 3, parameter entity is used in DTD

, use %entity name;use

4、可以将那些重复使用的值定义成实体，这样能减少代码的冗余度。

5、在外部DTD中，引用实体最好放在DTD底部，参数实体最好放在DTD顶部。

案例：

<!ENTITY % sex "男|女">
<!ELEMENT 班级 (学生+,作者)>
<!ELEMENT 学生 (名字,年龄,介绍)>
<!ELEMENT 作者 (#PCDATA)>
<!ATTLIST 学生
	性别 (%sex;) #REQUIRED
>
<!ELEMENT 名字 (#PCDATA)>
<!ELEMENT 年龄 (#PCDATA)>
<!ELEMENT 介绍 (#PCDATA)>
<!ENTITY writer "Switch">

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综合案例1：

XML3.dtd

<!ENTITY % sex "男|女">
<!ELEMENT 班级 (学生+,作者)>
<!ATTLIST 班级
	班次 CDATA "1班"
	编号 ID #REQUIRED
>
<!ELEMENT 学生 (名字,年龄,介绍)>
<!ELEMENT 作者 (#PCDATA)>
<!ATTLIST 学生
	地址 CDATA #IMPLIED
	授课方式 CDATA #FIXED "面授"
	学号 ID #REQUIRED
	班级编号 IDREF #REQUIRED
	朋友 IDREFS #IMPLIED
	性别 (%sex;) #REQUIRED
>
<!ELEMENT 名字 (#PCDATA)>
<!ELEMENT 年龄 (#PCDATA)>
<!ELEMENT 介绍 (#PCDATA)>

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XML3.xml

<?xml version="1.0" encoding="UTF-8"?>
<!-- 引入DTD -->
<!DOCTYPE 班级 SYSTEM "XML3.dtd"
[<!ENTITY writer "Switch">]>
<班级 编号="C1" 班次="1班">
	<学生  地址="湖南" 授课方式="面授" 学号="n1" 班级编号="C1" 朋友="n2" 性别="男">
		<名字>张三</名字>
		<年龄>20</年龄>
		<介绍>不错</介绍>
	</学生>
	<学生 授课方式="面授" 学号="n2" 班级编号="C1" 朋友="n1 n3" 性别="女">
		<名字>李四</名字>
		<年龄>18</年龄>
		<介绍>很好</介绍>
	</学生>
	<学生 授课方式="面授" 学号="n3" 班级编号="C1" 朋友="n2" 性别="男">
		<名字>王五</名字>
		<年龄>22</年龄>
		<介绍>非常好</介绍>
	</学生>
	<作者>&writer;</作者>
</班级>

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综合案例2：

XML4.dtd

<!ENTITY AUTHOR "John Doe">
<!ENTITY COMPANY "JD Power Tools, Inc.">
<!ENTITY EMAIL "jd@jd-tools.com">

<!ELEMENT CATALOG (PRODUCT+)>

<!ELEMENT PRODUCT
(SPECIFICATIONS+,OPTIONS?,PRICE+,NOTES?)>
<!ATTLIST PRODUCT
NAME CDATA #IMPLIED
CATEGORY (HandTool|Table|Shop-Professional) "HandTool"
PARTNUM CDATA #IMPLIED
PLANT (Pittsburgh|Milwaukee|Chicago) "Chicago"
INVENTORY (InStock|Backordered|Discontinued) "InStock">

<!ELEMENT SPECIFICATIONS (#PCDATA)>
<!ATTLIST SPECIFICATIONS
WEIGHT CDATA #IMPLIED
POWER CDATA #IMPLIED>

<!ELEMENT OPTIONS (#PCDATA)>
<!ATTLIST OPTIONS
FINISH (Metal|Polished|Matte) "Matte" 
ADAPTER (Included|Optional|NotApplicable) "Included"
CASE (HardShell|Soft|NotApplicable) "HardShell">

<!ELEMENT PRICE (#PCDATA)>
<!ATTLIST PRICE
MSRP CDATA #IMPLIED
WHOLESALE CDATA #IMPLIED
STREET CDATA #IMPLIED
SHIPPING CDATA #IMPLIED>

<!ELEMENT NOTES (#PCDATA)>

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XML4.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE CATALOG SYSTEM "XML4.dtd">
<CATALOG>
	<PRODUCT NAME="C&#39;estbon" CATEGORY="Shop-Professional" INVENTORY="Backordered" PARTNUM="10" PLANT="Chicago">
		<SPECIFICATIONS POWER="0" WEIGHT="555ml">SPECIFICATIONS</SPECIFICATIONS>
		<OPTIONS>OPTIONS</OPTIONS>
		<PRICE>2</PRICE>
		<NOTES>NOTES</NOTES>
	</PRODUCT>
</CATALOG>

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