About XML

eXtensible Markup Language

  • XML is a set of rules (you may also think of them as guidelines or conventions) for designing text formats that let you structure your data. XML is not a programming language. XML tags are not predefined in XML. You must define your own tags.
  • Like HTML, XML makes use of tags. XML uses the tags only to delimit pieces of data, and leaves the interpretation of the data completely to the application that reads it. In other words, if you see "<p>" in an XML file, do not assume it is a paragraph. Depending on the context, it may be a price, a parameter, a person
    • XML was designed to describe data, and to focus on what data is.
    • HTML was designed to display data, and to focus on how data looks.
  • XML files are text files.
  • Can embed XML inside of an HTML file using
            <xml> your xml here </xml>
      OR
            <xml src="file.xml"></xml>


  • Development of XML started in 1996
  • IE 5.0 and Netscape 6.0 started support of XML.
  • XHTML, an XML application, is the successor to HTML. XHTML has many of the same elements as HTML. The syntax has been changed slightly to conform to the rules of XML. A document that is "XML-based" inherits the syntax from XML and restricts it in certain ways
  • XML 1.0 is the specification that defines what "tags" and "attributes" are. Beyond XML 1.0, "the XML family" is a growing set of modules that offer useful services to accomplish important and frequently demanded tasks.

    Xlink describes a standard way to add hyperlinks to an XML file.

    XPointer and XFragments are syntaxes in development for pointing to parts of an XML document. An XPointer is a bit like a URL, but instead of pointing to documents on the Web, it points to pieces of data inside an XML file.

    XSL is the advanced language for expressing style sheets. It is based on XSLT, a transformation language used for rearranging, adding and deleting tags and attributes.

    DOM is a standard set of function calls for manipulating XML (and HTML) files from a programming language.

    XML Schemas 1 and 2 help developers to precisely define the structures of their own XML-based formats. There are several more modules and tools available or under development. Keep an eye on W3C's technical reports page.

© Lynne Grewe