This book constitutes the refereed proceedings of the 9th International Conference on Object-Oriented Information Systems, OOIS 2003, held in Geneva, Switzerland in September 2003.The 29 revised full papers and 11 revised short papers presented together with an invited paper and abstracts of 2 invited talks were carefully reviewed and selected from 80 submissions. The papers are organized in topical sections on evolution of OOIS, OOIS frameworks, patterns and components, object-oriented databases, XML on Web aspects, evolution, object-oriented design and architecture, and modeling of information systems.