Introduction to how to open xml files-XML/RSS Tutorial-php.cn

Extensible Markup Language (Extensible Markup Language, XML) is a markup language used to mark electronic documents to make them structural. It can be used to mark data and define data types , is a source language that allows users to define their own markup languages. XML is a subset of Standard Generalized Markup Language (SGML) and is well suited for Web transport. XML provides a unified method for describing and exchanging structured data independent of applications or vendors.

Format characteristics

XML is different from databases such as Access, Oracle and SQL Server. The database provides more powerful data storage and analysis capabilities, such as: data indexing, sorting, search, related consistency, etc. XML just displays data. In fact, the biggest difference between XML and other data representations is that it is extremely simple. This is a seemingly trivial advantage, but it's what makes XML unique.

The design difference between XML and HTML is: XML is used to store data, focusing on the data itself. HTML is used to define data, focusing on the display mode of the data.
The simplicity of XML makes it easy to read and write data in any application. This makes XML quickly become the only public language for data exchange. Although different application software also supports other data exchange formats, they will all be Supporting XML means that the program can more easily integrate with information generated under Windows, Mac OS, Linux and other platforms, and then it is easy to load XML data into the program and analyze it, and use Output results in XML format.

In order to make SGML user-friendly, XML redefines some internal values and parameters of SGML and removes a large number of rarely used functions. These complex functions make SGML complicated when designing websites. XML retains the structural functions of SGML, which allows website designers to define their own document types. XML also introduces a new document type, so that developers do not need to define document types.

Simple Syntax

SGML is often used to define document type definitions (DTD) for HTML, and it is also often used to write DTDs for XML. The problem with SGML is that it allows some strange syntax, which makes creating an HTML parser a big problem:
1 Some start tags do not allow end tags, such as the tag in HTML. An error will occur if a closing tag is included.
　2 Some start tags can optionally appear with an end tag or hide the end tag
　3 Some start tags require that an end tag must appear, such as the

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Introduction to how to open xml files