MapBase is a laboratory information system that has been supporting a high-throughput genome-mapping operation for the last three years. We chose to build MapBase around a C++-based OODBMS because, like CAD, CASE, and GIS applications, MapBase must be able to represent complex data and operations while providing fast response. However, MapBase also turned out to share many characteristics of classical information systems: it provides a central repository of carefully administered, mission-critical data used by clients written in manylanguages and running on a variety of hardware. In addition, our laboratory emphasizes continuous process re-engineering, with the result thatMapBase's schema must evolve rapidly in order to re ect the current experimental work ow. We discuss how the technical characteristics This work was supportedby funds from the National Institutes of Health, National Center for Human Genome Research, grant numberP50HG00098. PostScriptversionof thispaperavailable ...