XML DTD record

Introduction mode

Inside DTD

take DTD And XML Data definitions in the same document

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<!--  Inside DTD -->
<!DOCTYPE books[
	<!ELEMENT books (book)*>
	<!ELEMENT book (name,autor,price,desc)>
	<!ELEMENT name (#PCDATA)>
	<!ELEMENT autor (#PCDATA)>
	<!ELEMENT price (#PCDATA)>
	<!ELEMENT desc (#PCDATA)>
]>

<!-- xml  file  -->
<books>
	<book>
		<name>java</name>
		<autor>laolang</autor>
		<price>500</price>
		<desc>java  Books </desc>
	</book>
	<book>
		<name>php</name>
		<autor>php</autor>
		<price>400</price>
		<desc>php  Books </desc>
	</book>
</books>

external DTD

dtd

<?xml version="1.0" encoding="UTF-8"?>
<!ELEMENT books (book)*>
<!ELEMENT book (name,autor,price,desc)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT autor (#PCDATA)>
<!ELEMENT price (#PCDATA)>
<!ELEMENT desc (#PCDATA)>

xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE books SYSTEM "one.dtd">
<books>
	<book>
		<name>java</name>
		<autor>laolang</autor>
		<price>500</price>
		<desc>java  Books </desc>
	</book>
	<book>
		<name>php</name>
		<autor>php</autor>
		<price>400</price>
		<desc>php  Books </desc>
	</book>
</books>

public DTD

DTD Document structure

The first 1 Line is DTD Declaration part , And XML identical
0 To multiple comments , And XML identical
0 To more than one <!ELEMENT…> Definition , Every <!ELEMENT…> Define a XML Elements
0 To more than one <!ATTLIST…> Definition , Every <!ATTLIST…> by XML Element defines an attribute
0 To more than one <!ENTITY…>, Every <!ENTITY…> Define an entity
0 To multiple <!NOTATION…> Definition , Every <!NOTATION…> Define a symbol

this 4 Elements do not need to be nested within each other

ELEMENT

<!ELEMENT Element name Element type description >

The description of element types mainly includes the following 5 Kind of ：

1. Any type
   This element can be either a string , It can also contain other child elements , It can also be an empty element
2. A string value
   This element can only be a string , Cannot contain other child elements , Nor can it be an empty element
3. Empty elements
   This element can be an empty element , Neither can it contain child elements , Nor can it contain string values
4. Contains child elements
   It is necessary to define the order between child elements and the number of times that child elements appear in detail
5. Mixed type
   Appoint XML The value of an element can only be of certain types , Mixed types are stronger than constraints of any type

Any type

grammar : <!ELEMENT Element name ANY>
example :
DTD

<?xml version="1.0" encoding="UTF-8"?>
<!ELEMENT books ANY>

XML

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE books SYSTEM "one.dtd">
<books>
	books
</books>

XML

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE books SYSTEM "one.dtd">
<books/>

Empty elements

grammar : <!ELEMENT Element name EMPTY>
example :
DTD

<?xml version="1.0" encoding="UTF-8"?>
<!ELEMENT books EMPTY>

XML

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE books SYSTEM "one.dtd">
<books/>

character string

grammar : <!ELEMENT books (#PCDATA)>
example :
DTD

<?xml version="1.0" encoding="UTF-8"?>
<!ELEMENT books (#PCDATA)>

XML

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE books SYSTEM "one.dtd">
<books>
books
</books>

Mixed content

grammar ：<!ELEMENT Parent element name (#PCDATA | Subelement 1 | Subelement 2 | Subelement 3 ...)*>
Specifies that the contents of the parent element can be either ordinary strings , It can also be the child element specified by each child element name . It's worth pointing out , The child elements here 1、 Subelement 2 The vertical line between and subprime three does not indicate mutual exclusion , It just means that these child elements can repeat in disorder , The number of occurrences is unlimited .

dtd

<?xml version="1.0" encoding="UTF-8"?>
<!ELEMENT games (#PCDATA | game)*>
<!ELEMENT game (#PCDATA | name | type)*>
<!ELEMENT name (#PCDATA)>
<!ELEMENT type (#PCDATA)>

xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE games SYSTEM "one.dtd">
<games>
	 Games and programming are similar , It is a kind of interest 
	<game>
		<type> Action fighting </type>
		<name> Waiting soul </name>
		 Suitable for releasing tension 、 A dull feeling 
	</game>
	<game>
		 Relax 、 A good game to soothe your mood 
		<name> Thunder and lightning </name>
		<type> Flying shooting </type>
	</game>
	<game>
		<name> Thunder and lightning </name>
	</game>
	<game>
		<name> Thunder and lightning </name>
		<name> Waiting soul </name>
	</game>
</games>

Subelement

Ordered child elements

If you use an English comma as a separator between child elements , The defined order must be observed between the child elements

dtd

<?xml version="1.0" encoding="UTF-8"?>
<!ELEMENT games (game)*>
<!ELEMENT game (name,type)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT type (#PCDATA)>

xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE games SYSTEM "one.dtd">
<games>
	<game>
		<name> Waiting soul </name>
		<type> Action fighting </type>
	</game>
	<game>
		<name> Thunder and lightning </name>
		<type> Flying shooting </type>
	</game>
</games>

Mutually exclusive child elements

Mutually exclusive child elements indicate that only one of them can appear between a series of child elements . Use vertical lines to separate

dtd

<?xml version="1.0" encoding="UTF-8"?>
<!ELEMENT games (game)*>
<!ELEMENT game (name | type)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT type (#PCDATA)>

xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE games SYSTEM "one.dtd">
<games>
	<game>
		<name> Waiting soul </name>
	</game>
	<game>
		<type> Flying shooting </type>
	</game>
</games>

Sub element frequency

1. +: appear 1 Times or times
2. *: appear 0 Times or times
3. ?: appear 0 Once or once
4. No frequency specified : Can only occur and must occur once

Combine child elements

Use parentheses to enclose multiple child elements to form an element group , The child elements in the element group can be separated by commas , To indicate that the elements in the element group are in order , You can also use digital display to express mutual exclusion . You can use tags that represent frequencies to follow groups of elements , Used to indicate the frequency of occurrence of the element .

Unordered child elements

dtd There is no specific definition of unordered child elements , However, it can be realized with the help of element groups

<!ELEMENT games (game)*>
<!ELEMENT game(name|autor|price|type)+>
<ELEMENT name (#PCDATA)>
<ELEMENT autor (#PCDATA)>
<ELEMENT price (#PCDATA)>
<ELEMENT type (#PCDATA)>

Defining attributes

<!ATTLIST The element to which the attribute belongs Property name Attribute types [ Element constraints on attributes ] [ The default value is ]>

Not specified in “ Element constraints on attributes ” when , You must specify a default value for this property
When “ Element constraints on attributes ” yes #REQUIRED when , Default value... Cannot be specified
When “ Element constraints on attributes ” yes #IMPLIED when , Default value... Cannot be specified
When “ Element constraints on attributes ” yes #FIXED when , You must specify a default value

#REQUIRED : must
#IMPLIED : not essential
#FIXED : Fixed attribute

Attribute types

Entity

Symbol

done