XML

Extensible Markup language offers a means of representing less structured as well as structured data together with some level of self description. It is a well accepted technology that supports interoperability at a technical rather than a semantic level. Xquery, a language for querying XML, can combine documents, web pages, and links to relational databases. Query languages for semi-structured data usually adopt an underlying hierarchical data model, for instance a unidirectional graph. Required objects are specified by providing a path expression in a language that is quite usually intuitive. There are however inherent problems with hierarchical data model such, such as difficulty in representing many to many relationships .In spite of this the hierarchical model has been embraced by web community as a useful intuitive and practical structure.