Implementation of checkout/checkin mechanism on object-oriented database systems

The authors discuss the implementation of the checkout/checkin mechanism in object-oriented database systems. Objects are no longer modified directly in the public database. Each user has a private workspace and his/her tasks are performed in the workspace. When the tasks are done, the user checks in modified objects in the public database. They introduce several classes of long duration locks in order to allow users to lock objects for a long time. A composite object, version, versionable object, or simple object may be the granularity of a checkout operation. They effectively maintain the version derivation graphs in a public database and workspaces and manage checkouts of composite objects.