His research interests are databases in general, advanced databases for new and emerging applications, spatial databases, fuzzy spatial databases, and spatiotemporal and moving-objects databases. He is coauthor of a textbook on moving-objects databases, author of a monograph in the area of spatial databases, and author of a German textbook on implementation concepts for database systems, and has published about 60 articles, conference papers, and book chapters on database systems. He is on the editorial board of GeoInformatica.