This book constitutes the refereed proceedings of the 9th International Conference on Database and Expert Systems Applications, DEXA'98, held in Vienna, Austria, in August 1998. The 81 revised full papers presented were carefully selected from a total of more than 200 submissions. The papers are organized in sections on active databases, object-oriented systems, data engineering, information retrieval, workflow and cooperative systems, spatial and temporal aspects, document management, spatial databases, adaptation and view updates, genetic algorithms, cooperative and distributed environments, interaction and communication, transcation, advanced applications, temporal aspects, oriented systems, partitioning and fragmentation, database queries, data, data warehouses, knowledge discovery and data mining, knowledge extraction, and knowledge base reduction for comprehension and reuse.