This book presents an overview of the most fundamental aspects of the theory that underlies the Relational Database Model. As such it is self-contained though experience with formal models and abstract data manipulating on the one hand and with the practical use of a relational system on the other hand can help the reader. Such experience will offer the reader a better understanding of and a motivation for the different concepts, theories and results mentioned in the book. We have focussed on the most basic concepts and aspects of the relational model, without trying to give a complete overview of the state of the art of database theory. Recently a lot of books on databases in general and on the relational model in particular have been published. Most of them describe the use of database systems. 'Some clarify how information has to be structured and organized before it can be used to build applications. Others help the user in writing down his applications or in finding tricky ways to optimize the running time or the necessary space. Another category of books treat more fundamental and more general aspects such as the description of the relational model, independent of any implementation, the decomposition in normal forms or the global design of distributed databases. Few, however, are the books that describe in a formal way some of the subjects mentioned above.

On behalf of the AH 2004 Program Committee, we were pleased to welcome att- dees to Eindhoven for the 3rd International Conference on Adaptive Hypermedia and Adaptive Web-Based Systems. Similar to previous years, the number of research groups involved in research and innovative applications of personalization and adaptation functionalities has continued to grow, resulting in a further increase of 33% in the number of papers submitted to the conference, compared to the previous conference. From the 138 submissions we received, the program committee, in a rigorous review process, accepted 27 submissions (i.e., 20%) as full papers and 18 (i.e., 13%) as short papers. The large number of papers submitted generated a tremendous amount of work for the program committee members and the external reviewers, and we are immensely greatful for the effort they put into the process of selecting the very best papers. Together with three invited talks (by Emile Aarts, Philips Research, Candy Sidner, Mitsubishi Research, and Eric Horvitz, Microsoft Research), the AH 2004 - pers provide an excellent view on the successful approaches for innovative person- ization and adaptation functionalities in a variety of areas, including eLearning, eC- merce, mobile tourist guides and many more. They also show the integration of pers- alization functionalities being employed in Web environments, in ambient intelligence and intelligent agent contexts, and building upon adaptive hypermedia and Semantic Web technologies, Web search, Web services, social and peer-to-peer networks, and recommender systems, among others.