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6.3.1.3. Fact types dealing with attribu... > 6.3.1.3.3. Identification fact types - Pg. 169

148 CHAPTER 6 Fact models <term 1> < verb phrase>, in which term 1 signifies the entity (class): for example, F48. person smokes F49. person is deceased Such a fact type clearly has no reverse form. Note that the verb phrase must be intransitive, as distinct from a transitive verb phrase (one that requires an object as well as a subject, such as `employs' in `organization employs person'). Thus rule statements can include such sequences as a person who smokes, or if that person smokes. 6.3.1.3.2 Attribute fact types An attribute fact type is used to signify any other (non-Boolean) property or characteristic of an entity class (or object class). Such a fact type has the form <term 1> has <term 2>, in which term 1 signifies the entity class (or object class) and term 2 signifies the property or charac- teristic, with the reverse form <term 2> is of <term 1>: for example, F50. person has birth date/ birth date is of person Thus rule statements can include such sequences as a person who has a birth date that is earlier than 1/1/1950, a person whose birth date is earlier than 1/1/1950, or if the birth date of that person is earlier than 1/1/1950. 6.3.1.3.3 Identification fact types As we saw in Section 6.2.3.2.1, an identifier attribute is a particular type of attribute that exists purely to identify entity instances. An identification fact type is a particular variant of the attribute fact type that uses a more appropriate verb phrase to associate an entity class (or object class) with the relevant identifier attribute. Such a fact type has the form <term 1> is identified using <term 2>, in which term 1 signifies the entity class (or object class) and term 2 signifies the identifier, with the reverse form <term 2> identifies <term 1>: for example, F51. person is identified using social security number/ social security number identifies person