The World-Wide Web is currently the largest resource of information, which is easily accessible. However, the information it presents is not organized and a user has to search amongst hundreds and thousands of information sources for a single need. What is needed is an organized approach, so that information retrieval is simple and quick. The eXtensible Markup Language (XML) [Bray et al., 1998] is a new standard that supports data exchange on the World-Wide Web. It is sophisticated enough, so that complex real-world structures and relationships may be captured. At the same time it lends a structure to Web documents and the information that they contain.
XML is defined by Norman Walsh as "a markup language for documents containing structured information". The general set of rules for an XML document's tags and attributes (i.e. the structure) is defined in a Document Type Definition (DTD). An XML document without a DTD is a "well formed" document, if the basic tag constraints are followed, e.g. every start tag has an end tag, etc. With a DTD, validity of an XML document can be checked and it helps create a consistent structure for the type of document to be displayed. QT4XML (Query Tool For XML) exploits this feature to provide a user friendly visual query language to the user. Knowledge of the traditional query languages like SQL3 [Ullman and Widom, 1997] or OQL v.2 [Cattell et al., 1997] is not needed to use QT4XML.
This thesis addresses the problem of storing and retrieving XML documents as part of its prototype implementation. It also surveys the current work being done on query languages and tools for XML. Future development in terms of migrating the prototype database to Oracle8i [Oracle, 1998] is also discussed in the Appendix.