The Database and Expert Systems Applications - DEXA - conferences are dedi- cated to providing an international forum for the presentation of applications in the database and expert systems field, for the exchange of ideas and experiences, and for defining requirements for the future systems in these fields. After the very promising DEXA 90 in Vienna, Austria, we hope to have successfully established wjth this year's DEXA 91 a stage where scientists from diverse fields interested in application-oriented research can present and discuss their work. This year there was a total of more than 250 submitted papers from 28 different countries, in all continents. Only 98 of the papers could be accepted. The collection of papers in these proceedings offers a cross-section of the issues facing the area of databases and expert systems, i.e., topics of basic research interest on one hand and questions occurring when developing applications on the other. Major credit for the success of the conference goes to all of our colleagues who submitted papers for consideration and to those who have organized and chaired the panel sessions. Many persons contributed numerous hours to organize this conference. The names of most of them will appear on the following pages. In particular we wish to thank the Organization Committee Chairmen Johann Gordesch, A Min Tjoa, and Roland Wag- ner, who also helped establishing the program. Special thanks also go to Gabriella Wagner and Anke Ruckert. Dimitris Karagiannis General Conference Chairman Contents Conference Committee.