  According to strong demands for rapid and reliable software delivery,
co-existing database schema versions with multiple application versions are
reality to contribute them. Current database management systems do not support
co-existing schema versions in one database. Although a design of co-existing
schema based on updatable view tables was previously proposed, its flexibility
is limited due to pre-defined several restrictions to achieve data
synchronization among schemas and handling independent unsynchronized data in
each schema. In this preliminary report, we present a new approach for
co-existing schemas based on bidirectional transformation. We explain the
required properties to realize co-existing schemas, bidirectionality and
totality. We show that the co-existing schemas can be implemented
systematically by applying putback-based bidirectional transformation to
satisfy both the bidirectionality and the totality. While the bidirectionality
can be satisfied by applying bidirectional transformation, to satisfy the
totality, extra functions need to be introduced. How to derive these extra
functions is presented.
