What Does the File Extension XML Do?

The term XML, eXtensible Markup Language, is a type of semantic programming language that is used to organize and present data to a user. XML files use the .xml extension and can be read by most web browsers and certain computer program. These documents are used on many websites and widespread browser support for XML allows the data to be displayed without the user noticing any difference.

Significance

When XML was created, the most common way to display information on a website was through HTML, Hypertext Markup Language. HTML uses predefined tags to display and style data. For example, a paragraph in HTML is denoted by beginning the text with <p> and ending it with </p>. XML uses a similar tagging system which is based upon semantics rather than definition. While the tag <address> is irrelevant in HTML, it is perfectly acceptable in XML.

Function

XML is used in many web applications that involve dynamic, or changing, data. The RSS system uses a standardized model of XML. Each RSS feed uses the same semantic tags so any RSS reader can parse the feed for human viewing. XML is commonly used to transfer data between two websites. One website will publish an XML document with the information, and the other website will regularly query that page to retrieve the data. The semantic tags allow customer web programs such as these to design a meaningful page that is easy for the developers to work with.

Identification

Aside from the .xml file extension, XML files can be identified by the initial declaration. XML files typically begin with a <?xml?> tag, which contains the version and encoding information. This allows browsers that support the file type to appropriately render it. XML files will also contain tags that, typically, make sense even to an untrained user. These can include tags such as <title>, <link> and <category>.

Effects

The early adoption and widespread use of XML allowed for extremely dynamic, user friendly web pages. Its relative ease of use, when compared to other web based languages such as PHP and ASP, allows novice programmers to become familiar with web programming fundamentals. This opened up the field of web development to self taught users who lacked access to formal training in high-level languages.

Potential

XML files aid in the flow of information on the Internet. Websites that are based solely upon HTML are limited to readers who visit the website directly. By implementing XML, typically through RSS feeds, even small websites can be "syndicated" or broadcast to a much larger audience. Large sites, such as Technorati, congregate RSS feeds from thousands of websites, making that information available to a wide readership base. XML also allows for reader alerts, so subscribed users receive notices when new content is added to the website.