We are very grateful to Jelena Jovanovi , Nenad Krdžavac, and Colin Knight for a huge amount of help in preparing this book and for giving us many useful comments and suggestions. We would also like to thank all members of the GOOD OLD AI research group (http://goodoldai.org.yu) at the University of Belgrade, Serbia and Montenegro for providing us with a great environment and many useful ideas that enormously improved the quality of the book. Dragan Gaševi is very grateful to Marek Hatala, Tom Calvert, Griff Richards, and other colleagues from the LORNET research network at Simon Fraser University in Vancouver, Canada, for their great support and understanding.We thank Bran Selic of IBM Rational Software for agreeing to write the book's foreword. We are also very grateful to Jean Bézivin of the University of Nantes whose research in the filed of model-driven engineering inspired us to start exploring relations between MDA and ontologies. A special mention should be given to Ralf Gerstner of Springer-Verlag, who invited us to write this book and had a lot of patience in working with us. We are very thankful to