Database architecture and version control for group work

In order to progress team cooperative work, it is desirable that each member can not only refer to the shared resources, but also maintain his/her own private resources. In our previous paper, we proposed a database system in which users could maintain private data in their own private work spaces and use the shared data in a shared work space. In this paper, we propose a data management model where private and shared versions can be bound easily. Assume that, a user creates certain data and migrates a copy of the data to the shared work space. When the creator improves the data in the shared work space, he/she often refers the private versions left in the private work space. It is important to provide the whole history of versions.