The Entity Relationship (ER) and/or Enhanced Entity Relationship (EER) notation can be used to graphically represent action assertions. Action assertions are one of the three types of recognized business rules that control daily business operations. This graphical action assertion representation enforces constraints on the way data should be used by the organization and is implementation independent. An organization may have many business rules that need to be implemented to correctly control the daily operation of the business. Traditionally these business rules have been encoded into application programs that have been virtually unrecognizable, unmanageable, and inconsistent. Capturing business rules in such a way can lead to the business rules being inconsistent between various user applications. This approach places a heavy burden on the programmer, who must know all the constraints that an action may violate and must include checks for each of these constraints. An omission, misunderstanding, or error by the programmer will likely leave the database in an inconsistent state. In this paper the ER/EER notation will be used to define business rules at the conceptual level in a relational data model. Placing the business rules at the same level as the data has a natural appeal because the business rules are always about the data. The business rules are thus used to enforce database consistency that goes beyond foreign key relationships and delves into how an organization should operate its business.
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