当前位置：网站首页>20 minutes to learn what XML is_ XML learning notes_ What is an XML file_ Basic grammatical rules_ How to parse

20 minutes to learn what XML is_ XML learning notes_ What is an XML file_ Basic grammatical rules_ How to parse

2022-07-04 10:30:00 【Big bear loves to work】

XML Learning notes

1.XML What is it

1.1 brief introduction

The main function ： Realize data transmission between programs 、 The configuration file config.xml、 Store data as a small database
Canonical data format , The data is structured

1.2 what is XML？

XML： Extensible markup language
For transmitting and storing data , Instead of presenting the data
Labels must be customized

<root>
    <user> Dong Xiao D</user>
    <age>23</age>
</root>

XML and HTML The difference between
- HTML The label of cannot be customized 、XML The label can be customized
- HTML The grammar of is not strict 、XML The grammar of is very strict
- HTML Used to show data 、XML For storing and transmitting data

2. Rule of grammar

2.1 Basic grammar

must There are root nodes （ There can only be one ） The following is an error case

<root>
    <student> Nicola </student>
</root>

<root1>
    <student> Zhao si </student>
</root1>

XML The header statement is optional

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

be-all XML All elements must It's a pair of labels
Tag names are case sensitive
Labels cannot be crossed
Annotation method

<root>
    <user> Dong Xiaodong </user>
    <!--<age>23</age>-->
</root>

Special characters require entity escape characters
The name of the label can be the same

Namespace

Situations that cause naming conflicts ： Two Different documents Used the same Element name

Avoid naming conflicts by using prefixes

1. Define prefix

Namespaces pass through elements xmlns Attribute definitions
```
xmlns:ns="http://www.dzc.com"
```

Mode one ： When using the element with the same name, define the namespace it belongs to

<root>
    <ns:student xmlns:ns="http://www.dzc.com">
    	<stu> Dong Xiaodong </stu>
    </ns:student>
     notes ：ns Is a prefix that represents a namespace   student Is the element with the same name 
    <fs:student xmlns:fs="http://www.fzc.com">
        <stu> Feng Zhaocheng </stu>
    </fs:student>
</root>

Mode two ： Declare the namespace definition in the root element

<root xmlns:ns="http://www.dzc.com" xmlns:fs="http://www.fzc.com">
    <ns:student>
    	<stu> Dong Xiaodong </stu>
    </ns:student>
     notes ：ns Is a prefix that represents a namespace   student Is the element with the same name 
    <fs:student>
        <stu> Feng Zhaocheng </stu>
    </fs:student>
</root>

XML With LF Store newlines

2.2 Element attributes

Attributes are just some additional information that describes the tag

<root>
    <student>
        <user> Dong Xiaodong </user>
        <age>23</age>
    </student>

    <student>
        <user age = "23"> Dong</user>
    </student>
</root>

A tag can have multiple properties , Attribute values need to be enclosed in quotation marks
Basically not much use , Additional parsing code will be added

2.3 Use CDATA The syntax does not parse the specified text

<![CDATA[ Need text content that is not parsed ]]>

 for example ：
<root>
    <student>
        <user age = "23"> <![CDATA[a>b,c<d]]></user>
    </student>
</root>

When there are many special characters , Use CDATA grammar
CDATA Nesting not allowed

2.4 XML Of DTD and XML Schema

DTD and Schema It's all defined XML Document structure , however XML Schema More commonly used .

3. analysis XML

[C# operation XML Methods, - Solitary summer - Blog Garden (cnblogs.com)]:

[C++ in XML Read and write operations - htj10 - Blog Garden (cnblogs.com)]:

4. In life XML Case study

XMLX Journalism

<?xml version="1.0" encoding="ISO-8859-1"?>
<nitf>
	<head>
		<title>Colombia Earthquake</title>
	</head>
    
	<body>
		<headline>
			<hl1>143 Dead in Colombia Earthquake</hl1>
		</headline>
		<byline>
			<bytag>By Jared Kotler, Associated Press Writer</bytag>
		</byline>
		<dateline>
			<location>Bogota, Colombia</location>
			<date>Monday January 25 1999 7:28 ET</date>
		</dateline>
	</body>
</nitf>

summary

1.XML Mainly used for data exchange 、 Sharing and storage

2. Tree structure

3. All modern browsers use XML Parser , For reading and operation XML

4.DOM(Document Object Model) The file object model defines an access XML Standard method of

5.XMLHttpRequest Object provides a function of communicating with the server after the web page is loaded

6.XML Namespaces provide a way to resolve element name conflicts

7.CDATA The text in the area will be XML The parser ignores

The book follows ： Study XML DOM— analysis XML file

原网站

版权声明
本文为[Big bear loves to work]所创，转载请带上原文链接，感谢
https://yzsam.com/2022/02/202202141418111803.html