DTD modeling

Catalog

What is? DTD？

What is? XML？

XML What is it for ？

XML The relatives of ：

1.XML My good brother ——HTML

2.XML My best friend ——JSON

XML Data structure of —— Tree structure ：

XML Standard format ：

  Element definition ：

1. stay XML Add DTD Statement ：

2. The classification of elements ：

3. The limitation of elements ：

Attribute definitions ：

1. grammar ：

2. Attribute types ：

3. Property description ：

Case study ：

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What is? DTD？

          Document type definition (Document Type Definition) Is a set of syntax rules about markers established for data exchange between programs . It is the standard general purpose markup language (SGML) And extensible markup language (XML)1.0 Part of the version specification , Documents can be based on DTD Syntax rules verify whether the format conforms to this rule . The document type definition can also be used as a guarantee standard common markup language 、 The legitimacy of XML document format , You can check whether the document conforms to the specification by comparing the document with the document type definition file , Are elements and labels used correctly . The file instance provides a data exchange format for the application .

PS： In short ,DTD It's used to constrain XML Document , Make it used under certain specifications , except DTD Outside technology , also Schema technology , Also for constraints XML Document .

What is? XML？

XML,Extensible Markup Language, Extensible markup language . The suffix of the file is .xml. It's like HTML Is used to display data ,xml The role of is Transfer and store data Of .

XML What is it for ？

In fact, it's plain ,xml It is convenient for different applications 、 Data sharing and communication between different platforms .

As shown in the figure below ：

  The functions of the specific points are ：

(1) It can be used as a simple database , Store and retrieve data ;

(2) Transfer files in the agreed format ;

(3) Make software configuration files .【 The configuration file ： Save the file of software settings 】

XML The relatives of ：

1.XML My good brother ——HTML

① Let's take a look at their birth order ：

  Actually XML I was born to perfect HTML Defects and localities of .

② Differences in use ：

Compare content	HTML	XML
effect	Display the data	Transfer and store data
grammar	No right-hand requirements	Nesting required 、 pairing , And follow DTD Tree structure of
Space	When more than one is entered, only One	Enter several to display several
Relationship with database	No direct connection	It can correspond and transform with relational and layered databases
Case sensitive	Indistinguishes	Strictly distinguish between

2.XML My best friend ——JSON

Is this relationship easier to understand ： My brother was born to a mother , But girlfriends are not .

JSON,Javascript Object Notation,js Object notation . The function is also to store and exchange text information .

A comparison of the two ： because ,JSON Use the format of key value pairs , therefore ,JSON Than XML smaller 、 faster 、 Easier to parse ,so, It is also more popular .

The scope of action of both ：JSON It is suitable for simple value transfer ,XML It is suitable for wider value transmission .

XML Data structure of —— Tree structure ：

  Be careful ： Like a tree with only one root ,XML There can only be one root element .

XML Standard format ：

  Element definition ：

1. stay XML Add DTD Statement ：

<!DOCTYPE root[]>

2. The classification of elements ：

① Empty elements

<!ELEMENT element-name EMPTY>

② Text elements

<!ELEMENT element-name (#PCDATA)>

③ Mixed elements  

<!ELEMENT element-name (e1,e2)>

3. The limitation of elements ：

ps: The default number of times is ？ 

Attribute definitions ：

1. grammar ：

<!ATTLIST element-name att-name type desc>

2. Attribute types ：

ID	Require all tags in the document ID Property values of types must not be the same
Enumerated	You must select... From the enumerated data types , Such as (true|false), You can also leave the type blank , Written directly (true|false)
CDATA	Property values of this type cannot contain “<” and “””, But entities can appear in this string
IDREF	Used to represent XML A type of relationship between tags in a document , Its value must be the value of a tag defined in the document ID Property value of type
IDREFS	Be similar to IDREF, But you can reference more than one ID, Multiple ID Space between

3. Property description ：

• #REQUIRED： Required
• #IMPLIED： Not required
• The default value is ： Only when the attribute type is Enumerated When ,desc To specify the default value .

Case study ：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE persons[
	<!ELEMENT persons (person+)>
	<!ELEMENT person (name,age,contact,br*)>
	<!ELEMENT name (#PCDATA)>
	<!ELEMENT age (#PCDATA)>
	<!ELEMENT contact (phone|email)>
	<!ELEMENT br EMPTY>
	<!ATTLIST person
	  pid ID #REQUIRED
	  sex ( male | Woman ) ' male '
	  qq CDATA #IMPLIED
	  parent IDREF #IMPLIED
	>
]>
<persons>
	<person pid="p1" sex=" male " qq="aaa" parent="p2">
		<name> Zhang Xiaoming </name>
		<age>10</age>
		<contact>
			<phone>1234567</phone>
		</contact>
		<br/>
	</person>
	<person pid="p2">
		<name> Zhang Daming </name>
		<age>35</age>
		<contact>
			<email>[email protected]</email>
		</contact>
	</person>
</persons>

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