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Defining the entities in your logical model is essential to the clarity of the model and is a good way to elaborate on the purpose of the entity and clarify which facts you want to include in the entity. Undefined entities or attributes can be misinterpreted in later modeling efforts, and possibly deleted or unified based on the misinterpretation.
Writing a good definition is more difficult than it may seem at first. Everyone knows what a CUSTOMER is, right? Just try writing a definition of a CUSTOMER that holds up to scrutiny. The best definitions are created using the points of view of many different business users and functional groups within the organization. Definitions that can pass the scrutiny of many, disparate users provide a number of benefits including:
Most organizations and individuals develop their own conventions or standards for definitions. In practice you will find that long definitions tend to take on a structure that helps the reader to understand the “thing” that is being defined. Some of these definitions can go on for several pages (CUSTOMER, for example). As a starting point, you may want to adopt the following items as a basic standard for the structure of a definition, since IDEF1X and IE do not provide standards for definitions:
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