What Is XML? A Quick Refresher

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XML (Extensible Markup Language) is an emerging technology used to structure and describe data. It is a derivative of Standard Generalized Markup Language (SGML), much like HTML. The difference between HTML and XML is that HTML is structured and defined with common specifications. In other words, in HTML, all tags are predefined and have meaning. In XML, you define your own tags.

HTML is designed for displaying information in a browser, and that is truly its limitation. With HTML, you can define how information should look in a browser, but it is meaningless beyond that. With XML, you can define data that can be displayed in a browser, or that can be used by your application in the same manner that data from a database can be used. In other words, XML is used to describe data.

The .NET Framework and ADO.NET use XML heavily under the covers. Data that is pulled from a database into your application using one of the ADO.NET Managed Providers is persisted as XML, transmitted, and rematerialized as useful data. The real advantage in this is that XML is text based and nonproprietary. This means that any system that can read text can work with XML, whether the XML is parsed and used, or simply saved to the file system or passed on to another system. This opens the .NET Framework to being compatible with disparate systems, the true power of .NET.

The System.Xml namespace includes several classes that make working with XML, as well as XSL Transform (XSL/T) stylesheets, very easy. Creating, reading, and writing XML data becomes as simple as constructing instances of classes, altering properties, and making a few method calls. Additionally, the ASP.NET Xml server control enables the display of XML data in a browser, and the use of XSL/T stylesheets on that data, with no code other than the server control tag.

Note

To learn more about using XML in ASP.NET, read XML for ASP.NET Developers by Dan Wahlin, Sams Publishing, ISBN 0-672-32039-8.

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