Extensible Markup Language (XML) was first brought into the spotlight in 1996 by the World Wide Web Consortium (WC3). XML is a markup language just like HTML, but without the fixed format. A markup language provides words and tags that describe a document and identify the pieces. HTML is about presentation while XML works to store and transport structured data. All XML files follow some basic rules for syntax and form. The simplicity of the language allows the author to develop a structure that focuses on the data with customized element tags. XML improves the functionality of the Internet by providing files that are flexible and adaptable.
By itself, XML does not display data. That is not the purpose of the language. XML is a box that makes the data portable and accessible. In order to display the information contained in an XML document, you must create formatting instructions. A Document Type Definition (DTD) provides validation instructions that exist internally, as part of the XML file, or as a separate linked file. A schema, or XSL, is a style sheet that gives information to validate the XML data as well as formatting instructions to create an output stream. There are a number of subsets within the XML language that make the process of formatting data possible. Included in the components of XML are XSLT, XLink, XQuery and XPath, just to name a few.
XML is a simple language that most anyone can master. It does not carry the same rules and strict syntax that other Internet languages require. This makes it a good choice for novices and experts alike. Once you have the basic rules down pat, creating a well-formed XML file will provide a straightforward way to organize and update data for web pages.