This paper presents an equational formulation of an object-oriented data model. In this model, a database is represented as a system of equations over a set of oid's, and a database query is a transformation of a system of equations into another system of equations. During the query processing, our model maintains an equivalence relation over old's that relates old's corresponding to the same ''real-world entity.'' By this mechanism, the model achieves a declarative set-based query language and views for objects with identity. Moreover, the query primitives are designed so that queries including object traversal can be evaluated in a data-parallel fashion.