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3.3.2. Expressing rules in natural language > Assertions - Pg. 70

3.3 Recent developments 49 5. An enumeration: <det> < result> must be chosen from the following {open|closed|} enumeration: <enum list>. For example, "The Gender of a Person must be chosen from the following closed enumeration: `Male', `Female'." Assertions The assertions technique described in (Simsion and Witt, Data Modeling Essentials, 2004) is designed to provide a complete verbal description of a data model and associated constraints using the appro- priate templates for each type of data model artifact or constraint being described. These templates use the notation described in Section 9.1.1 of Chapter 9. The types of assertions relevant to business rules include the following: 1. entity class assertions: a. entity class definitions, of the form {A|An} <Entity Class Name> is <Entity Class Definition>. For example, "A Customer is a business or a person that has purchased at least one product." b. subtype definitions, of the form {A|An} <Entity Class Name> is a type of <Superclass Name>,