In this paper, we present the design of the EXTRA data model and the EXCESS query language for the EXODUS extensible database system. The EXTRA data model includes support for complex objects with shared subobjects, a novel mix of object- and value-oriented semantics for data, support for persistent objects of any type in the EXTRA type lattice, and user-defined abstract data types (ADTs). The EXCESS query language provides facilities for querying and updating complex object structures, and it can be extended through the addition of ADT functions and operators, procedures and functions for manipulating EXTRA schema types, and generic set functions EXTRA and EXCESS are intended to serve as a test vehicle for tools developed under the EXODUS extensible database system project.
