What is XML?

Before learning about XML, we must first find the original sin issue of HTML. Only by knowing the defects in HTML can we better understand the role of XML.

Original Sin of HTML:
All data interpretation problems cannot be solved. Such as audio and video files, chemical formulas, music symbols, and other types of content.
Performance problems. If you need to download the entire file, you can start searching for the file.
Poor scalability, elasticity, and ease of use.

In order to solve the above problems, experts used SGML for simplified production and, based on the development experience of HTML, produced a set of rigorous rules for use, but simple description Data Language: XML. XML is born in this context-is there a more neutral way for the consumer to decide on its own how to digest and present the information provided by the slave server? The purpose of XML is to provide a mechanism to accurately describe information, so as to make up for the characteristics that HTML is too expressive and oriented.

XML (Extensible Markup Language) can be used to expand the markup language. Like HTML
Generalized Markup
Language ). XML is cross-platform in the Internet environment and relies on content technology. It is a powerful tool for processing structured document information. Extended Markup Language
XML is a simple data storage language that uses a series of simple tags to describe data. These tags can be conveniently created, although XML occupies more space than binary data, XML is extremely easy to master and use.

XML and access, Oracle and SQL
Different databases such as server provide more powerful data storage and analysis capabilities, such as data indexing, sorting, search, and consistency. xml only displays data. In fact, XML
The biggest difference from other data forms is that it is extremely simple. This is an advantage that looks a little refined, but it makes XML different.

 
XML makes it easy to read and write data in any application, which makes XML a data
The only public language for data exchange, although different applications also support other data exchange formats, but soon they will support XML, which means that the program can be easier than windows,
The combination of information generated in Mac OS, Linux, and other platforms makes it easy to load XML data into a program, analyze it, and output results in XML format.

To make SGML more user-friendly, XML redefined some of sgml's internal values and parameters, removing a large number of rarely used functions. These complex features complicate SGML when designing websites. XML retains the structured functions of SGML, so that website designers can define their own document types. xml also introduces a new document type, so that developers do not need to define document types.

The above is just a comparison between the definition and definition of XML. To put it simply, XML is a data description language. Although it is a language, it does not have the basic functions of common languages-it is recognized and run by computers. It can only be interpreted in another language to achieve the desired effect or be accepted by the computer.

If you are new to XML, you may not be able to understand what XML is. Maybe, you can understand what XML is from another angle; understand XML from the application side, and know what XML can do to understand it, which should be more helpful to you than the more empty definition.

XML applications are mainly divided into two types: document and data. The following describes several common XML applications:

1. Custom XML + XSLT => HTML, one of the most common document applications. XML stores the XML data of the entire document, and XSLT converts and parses the XML, combines the HTML tags in XSLT, and finally becomes HTML, which is displayed on the browser. A typical example is the post on csdn.

2. XML, as a micro-database, is one of the most common data-type applications. We use the relevant XML APIs (MSXML Dom, Java
Dom, etc.) to access and query XML. The implementation of the message board often shows that XML is used as the database. At the same time, I want to tell some new people, databases and database systems. These two concepts are not
. The impact of XML on the database system is introduced here. In the new version of traditional database systems, XML has become a data type. Compared with "traditional", it is a new form of database, completely
A database system based on XML technologies. Currently, exist is a well-known exist.

3. As the carrier of information transmission. Why is it a carrier? Although these applications are still in XML format, they have developed a specific format. The most typical is
Web
Service, which encapsulates data into XML for transmission, but the XML here already has a specific specification, that is, soap. However, I still have to say That Ajax and Ajax applications also have
Some applications use custom XML as data, but it is not an industrial standard.

4. Application configuration data. The most typical is the Web. xml used when the J2EE Web server is configured. This application is easy to understand. We only need to store the required data
XML, and then load the program running in our application, and perform corresponding operations based on different data. This is actually a bit similar to Application 2. The difference is that the data changes in the database are normal, and the configuration
Information is often relatively static and lacks changes.

5. XML format of other documents. Such as Word and Excel.

6. Save the ing between data. Such as hibernate.

In these common applications, we can also divide them into custom XML and specific XML based on their wide application scope. 1 and 2 are the categories of custom XML; 3 to 6 are specific XML, or XML extensions.

In short, XML is an abstract language, which is not as specific as traditional programming languages.

From: http://news.csdn.net/n/20081208/121574.html