Several types of data organizations have been proposed in the literature for object-oriented and relational databases. In studying these organizations, there appears to be no underlying common basis on which they can be compared. Many of these organizations impose restrictions on their applicability that seem unnecessary or ad-hoc. We present a unified framework for physical database storage. We show that most existing data organizations follow naturally as special cases of this framework. Furthermore, this framework permits the specification of new types of data organization that have not been proposed or that cannot be described in existing systems, yet appear to be useful.