Logical and physical support for heterogeneous data. Sihem Amer-Yahia, Mary Fernandez, Rick Greer and Divesh Srivastava. Heterogeneity arises naturally in virtually all real-world data. This paper presents evolutionary extensions to a relational database system for supporting three classes of data heterogeneity: variational, structural and annotational heterogeneities. We define these classes and show the impact of these new features on data storage, data-access mechanisms, and the data-description language. Since XML is an important source of heterogeneity, we describe how the system automatically utilizes these new features when storing XML documents.