Notes
- Martin , James and Odell , James J. 1995 . Object-Oriented Methods. , Englewood Cliffs , NJ : PTR Prentice-Hall, Inc. .
- Halpin , Terry . 1995 . Conceptual Schema & Relational Database Design. , Sydney : Prentice-Hall .
- Tufte , Edward R. 1990 . Envisioning Information. , 53 Cheshire , Connecticut : Graphic Press .