xml programming (1)-xml syntax

XML programming

The standard

sgml Standard General Markup Language 1985

html Hypertext Markup Language 1993, to solve the problem of different platforms and different browsers accessing the same web page

xml extensible markup language 1998

2. The definition of xml

Extensible markup language is a markup language used to mark electronic documents to make them structural. It can be used to mark data and define data types. It is a source language that allows users to define their own markup language.

3. The difference between xml and html

html: display data

html：

武松

xml：

武松

html binds data and format together

Different browsers interpret HTML differently: IE, Firefox.

HTML syntax requirements are not strict

etc.

4. The main purpose of xml

Interaction between programs Communication

serves as the configuration file of the program

stores data

standard data format

2. xml quick start

describes a person’s information

30

Comment

CDATA area

Special characters

Processing instructions

Document declaration:

You need to use a document declaration to declare the XML document first

The simplest syntax:

encoding

Specify the encoding format

standalone

Whether the current document is independent yes/no

Element:

A tag is divided into a start and end tag (cannot be omitted)

Error: Content

Correct:

Several sub-tags can be nested in one tag, but all tags must be nested reasonably. Cross-nesting is not allowed

Error:

Correct:

An XML document must have one and only one root tag, and other tags are sub-tags of this root tag

Element-naming:

The name of an element (tag) can contain letters, numbers, minus signs, underscores and English Periods

are strictly case-sensitive;

and represent two tags

can only start with letters or underscores;

A123

_123

Error: 12a

cannot start with xml (or XML, Xml, etc.)

Error at the beginning: Colons cannot be used between name characters: Error:

Element attributes

An element can have multiple attributes

Attribute values ​​must be enclosed in quotes (single quotes or double quotes)

The naming convention of attribute names and elements The naming convention is the same

The attributes in the element are not allowed to be repeated

Error

The information represented by the label attribute can also be changed to be described in the form of sub-elements

< ;person id='100'> can be changed to

100

Notes

There can be no comments before the XML declaration

Comments cannot be nested,

Error>

CDATA area ：

CDATA：Character Data

Function: treat labels as ordinary text content

Syntax:

Special characters:

Some special characters must be escaped if they are to be displayed in the body content of the element.

Processing instructions:

Function: Used to instruct the software how to parse XML documents.

Syntax: Must start with "".

Commonly used processing instructions:

xml instruction

xml-stylesheet instruction

#p#xml tutorial-xml dtd constraint#e#

DTD constraint

1. What is a constraint? In XML technology, you can write a Document to constrain an XML writing specification. This document is called a constraint.

Well-formed XML: XML that follows XML syntax

Valid XML: XML that follows a constraint document

A document that follows xml syntax is called legal

An xml document that follows a constraint document is called reasonable

Legal xml is not necessarily reasonable

reasonable must be legal

2. Common constraints

XML DTD

XDR

SOX

XML Schema

3. What is dtd

lDocument Type Definition Document type definition

Constraint XML writing specifications

4. Location of dtd storage

In the file: You can place the dtd constraints in the current xml file

External file: You can also put the constraints in an external .dtd In the document

5. Quick start with dtd

6. How to detect whether our xml document complies with dtd constraints? ? ?

Program

ActiveXObject("Microsoft.XMLDOM") //Instantiate the xmldom object

doc.validateOnParse //Whether to enable verification

doc.async //Whether it is asynchronous

doc.load() //Loading

doc.parseError.reason //Error message

doc.parseError.line //Error line number

Software iexmltls This small plug-in can detect whether the document you wrote is a valid xml' document under IE.

7. How to reference external dtd

DOCTYPE statement:

//Externally introduce dtd document

Eight. dtd syntax

definition element

definition Attributes

define entities

1. Define elements

Syntax:

Usage rules:

(#PCDATA): text data

EMPTY: empty

ANY: Any

(child element): Appears only once

(child element 1, child element 2,...): Specifies child elements in order

(child element +): Appears at least once

(child element*) : Child element can appear any number of times

(child element?) : Child element appears 0 or 1 times

(child element 1 | child element 2) : Choose any one

2. Define attributes

Syntax:

Attribute type:

CDATA: Text

(en1|en2|……): Choose one of the values ​​

ID: The value is unique

Default value:

#REQUIRED Non-empty The attribute that uses this modification must be written

#IMPLIED Optional Can be written or not

#FIXED Fixed value You can not specify it. If specified, only this value can be used

Default value If a value is specified, the specified value will be used as the standard. If not specified, the default value will be used

3. Define the entity

Defining an entity is to specify a name for a piece of content. When using this name, you can refer to the content it represents.

Internal entity

External entity

Define internal entity

Definition syntax:

Quotation syntax:

&Entity name;

Definition external Entity

definition syntax:

Reference syntax:

&entity name

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