It is often easier to visualize a complex system rather than decipher long textual descrip- tions of a users’ requirements specification. We use Entity–Relationship (ER) diagrams to represent entities and how they relate to one another more easily. Throughout the database design phase, we recommend that ER diagrams should be used whenever necessary to help build up a picture of the part of the enterprise that we are modeling. In this book, we have used the latest object-oriented notation called UML (Unified Modeling Language) but other notations perform a similar function (see Appendix F).