XML

= Extensible Mark-up Language (XML) = toc XML is a computer markup language. Markup languages are used to convey information in a standardized way across different technologies, softwares and systems. This activity is particularly meaningful to librarians who have been developing standardized ways of recording and sharing information about library resources since before the birth of the computer. XML can extend the librarian's ability to generate and share any type of information with computer systems that can analyze it and present it meaningfully to users. XML also lays the foundation of the Semantic Web.

What does "Extensible" mean?
The unique contribution of XML is that it is a “modular” language, perhaps more aptly called a grammar. It was designed for optimum flexibility so that anyone can create their own subset of XML. XML provides a syntax which can be used with various vocabularies to meet application-specific needs. In the library arena, two common applications of XML are XHTML – a language which browsers read to present web pages to users, and MARCXML – a language which incorporates MARC bibliographic records into a more comprehensive data structure. Eric Lease Morgan lists more library applications of XML. Other common applications of XML are RSS and RDF.

What's the difference between XML, XHTML, and HTML?
In oversimplified terms, XML and HTML are both descendants of the first markup language, SGML. XHTML is a variant of HTML which conforms to XML's more stringent syntax. XHTML could thus be considered a “child” of HTML and XML, as illustrated by the “family tree” below. Tor Arne Dahl offers a more precise summary.

Rules of XML
Writing XML is simple. The following example illustrates the basics of XML syntax.
 * 1) This is the Document Type Declaration (DTD). It identifies the document as XML.
 * 2) All XML documents have one root element. In this case, “house.” It has two rooms as child elements.
 * 3) Text enclosed between “< - - !” and “- - >” are comments. Only people read them.
 * 4) Every element must have an open tag “ ” and a close tag “ .”
 * 5) “sink,” “toilet,” “bed,” and “chair” are empty elements. They open and close in the same tag.
 * 6) “doors,” “name,” “size,” and “groundfloor,” are attributes. Their name is displayed here in red and their value in purple.

What does XML do?
Unlike programming languages, XML does not “do” anything. It conveys information for another technology to do something with. To use my house illustration above, someone may write a program that converts that document into a blueprint image. Someone else may design a real-estate database that stores that document and allows househunters to search for it.

XML and the Semantic Web
The Semantic Web is based on the idea of making content readable not only by human beings, but also by computers. XML provides a common framework for computers to “understand” not only the structure, but the content of documents. The beauty of XML is that the same information can be easily accessed and used by many different technologies, softwares, and systems to accomplish goals that have not yet been imagined.

Resources

 * 1) Dahl, T. A. (2011, August 22). XML: Introduction and well-formed documents. //Oslo and Akershus University College of Applied Sciences//. Retrieved November 20, 2011, from []
 * 2) Lane, J., Moscovitz, M., & Lewis, J. R. (2008). //Foundation Website Creation with CSS, XHTML, and JavaScript//. New York: Springler-Verlag.
 * 3) Morgan, E. L. (2008, May 18). XML in libraries: A workshop. //Infomotions//. Retrieved November 20, 2011, from []
 * 4) Refsnes Data. (n.d.). XML Introduction - What is XML? //w3schools//. Retrieved November 20, 2011, from []