Legality of XML-Schema Type Hierarchies

The eXtensible Markup Language (XML) and XML-Schema are increasingly becoming the languages of choice to exchange data and describe data across the Internet, respectively. In this perspective, much of the database research focus is shifting from the traditional database models to the semistructured data and XML. In this paper, a formal framework supporting the design of XML-Schema type hierarchies has been proposed, by following and revisiting the database approach. In particular, the notion of a legal XML-Schema type hierarchy has been formally given and an algorithm for checking the legality of type hierarchies has been proposed.