About XML file

 A .xml file is just a .txt file. The different is that it adds many tags inside. These tags are used to add extra information inside, except for data.

  Currently, XML is widely used in word processor and database software. For example, in Microsoft Word, [File]--[Save As] to save the content into a .xml file. Then, it contains all the format information, except for the content. If you save Microsoft Word as a .txt file, you can only see your content, but all the formats are lost. This is the advantage of XML files. Besides, you do not have to use Microsoft Word or Microsoft Word Viewer to open and read them. You can open a .xml file with Windows Notepad, and all kinds of operating system and application programs. 

  Another example is database software, including Oracle, SQL Server, Firebird, MySQL and so forth. You can export the data from databases into xml files. As a result, the .xml files can contain the columns and rows of tables, except for data. It is much better than exporting data into .txt files. Later, you can import the .xml files into the databases with ease.

  XML tags are not fixed. Every one can use different tags. They are quite different from the tags of Web pages. People just need to guarantee that left and right angle brackets must include the attributes. Besides, XML files are mostly created by software, while Web pages are mostly created by hand. As a result, XML files have little errors, but Web pages have various and obvious errors. 

  Currently, standard XML tags of word processors have been created, although businessmen and politicians control them. It is called OOXML. As a result, different word processors can use the same tags to define the same formats. It means that, through the .xml files, you can change the files into Microsoft Word and OpenOffice, without any lost of formats. You can save a .docx file as .xml file through Microsoft Word, and then open it with OpenOffice. Finally, save the .xml as a .odt file. The .xml files play the role of a bridge.

  Database software is not so lucky. At present, Oracle, SQL Server, Firebird, MySQL use their own tags to define columns and rows of tables. As a result, you can hardly exchange data in different database software.  For example, you can export the data from SQL Server into .xml files, but can hardly import them into MySQL. You have to enter the data by hand repeatedly, inefficiently and unreliably. Maybe, you have to waste much money to employ many people to do this simple work.