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This paper presents a brief overview of data management using the Extensible Markup Language (XML). It presents the basics of XML and the DTDs used to constrain XML data, and describes metadata management using RDF. It also discusses how XML data is queried, referenced, and transformed using stylesheet language XSLT and referencing mechanisms XPath and XPointer. 1 Describing XML Data The Extensible Markup Language (XML) [BPSM98] models data as a tree of elementsthat containcharacter dataand haveattributescomposed of name-value pairs. For example, here is an XML representation of catalog information for a book: <book> <title>The spy who came in from the cold</title> <author>John <lastname>Le Carre</lastname></author> <price currency="USD">5.59</price> <review><author>Ben</author>Perhaps one of the finest...</review> <review><author>Jerry</author>An intriguing tale of...</review> <bestseller authority="NY Times"/> </book> Text delimited by angle brackets ( <...>) is markup, while the rest ischaracter data. (Here, and in the rest of this paper, we introduce concepts informally as needed for our discussion; for formal specifications, see [W3C99].) Elements may contain a mix of character data and other elements; e.g., the book element contains the text “Here are some...” in addition to elements such as title andprice . The element named title contains character data denoting the book title and is contained in the book element. Similarly, the element price contains character data denoting the book’s price. This element also has an attribute named currency with valueUSD, represented using the syntax ttribute-name="attribute-value" within the element’s start-tag. In general, element names are not unique; e.g., the book element in our example contains two review elements. However, attribute names are unique within an element; e.g., the price element cannot have another attribute named currency. The syntax permits an empty element <bestseller></bestseller> to be represented more concisely as<bestseller/> . XML documents are called well-formedif they satisfy simple syntactic constraints, such as proper delimiting of element names and attributes and proper nesting of start and end tags. Copyright 1999 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. Bulletin of the IEEE Computer Society Technical Committee on Data Engineering