A microcomputer implementation of an ER query interface

A query language has been defined in which users graphically manipulate Entity-Relationship (ER) diagrams to formulate queries involving computations [3]. In this paper we present a method of implementing this ER query language as an interface for a relational Database Management System. The approach is based on interactive manipulation of ER database schemas and generation of SQL expressions for an underlying relational database. The graphical query formulation process is formally defined. We assume that the information reflecting the current state of the query formulation process is maintained in a formal model. The model described in [3] is significantly modified and extended. The information included in the extended model allows an ER diagram corresponding to the current state of the query to be displayed on the terminal screen. It is also used to generate an equivalent SQL expression for a relational database. The integrity constraints for the formal model are specified.