In order to meaningfully contribute to the formal foundations of the Web, database theory has embarked upon a fascinating journey of rediscovery. In the process, some of the basic assumptions of the classical theory had to be revisited, while others were convincingly reaffirmed. There are several recurring technical themes. They include extended conjunctive queries, limited recursion in the form of path expressions, ordered data, views, incomplete information, active features. Automata theory has emerged as a powerful tool for understanding XML schema and query languages. The specific needs of the XML scenario have in turn provided feedback into automata theory, generating new lines of research. The Web scenario is raising an unprecedented wealth of challenging problems for database theory - a new frontier to be explored.
展开▼
