Knowledge from Semi-structured Information Sources

It is a pleasure to acknowledge the people who supported me during this work. First of all a special thanks is for Domenico Ursino who has never been just a supervisor but a great friend for me. My full gratitude goes to Luigi Palopoli who, with Domenico, has been a careful advisor and co-author of many papers; he supported me not only throughout the fulfillment of this work but also during some difficult moments of my life.