The authors describe the object-oriented design and implementation of an extensible schema manager for object-oriented databases. The open class hierarchy approach has been adopted to achieve the extensibility of the implementation. In this approach. the system meta information is implemented as objects of system classes. A graphical interface for an object-oriented database scheme environment, GOOSE, has been developed. GOOSE supports several advanced features which include schema evolution, schema versioning, and DAG (direct acyclic graph) rearrangement view of a class hierarchy. Schema evolution is the ability to make a variety of changes to a database scheme without reorganization. Schema versioning is the ability to define multiple scheme versions and to keep track of schema changes. A novel type of view for object-oriented databases, the DAG rearrangement view of a class hierarchy, is also supported.>