While the contents of databases can be easily changed, their organization is typically extremely rigid. Some databases relax the rigidity of database organization somewhat by supporting simple changes to individual schemas. As described in this paper, OTGen supports not only more complex schema changes, but also database reorganization. A database administrator uses a declarative notation to describe mappings between objects created with old versions of schemas and their corresponding representations using new versions. OTGen generates a transformer that applies the mappings to update the database to the new definitions, thus facilitating improvements in performance, functionality, and usability of the database.¹