130 CHAPTER 6 Fact models weight being recorded for any passengers by any airline (although it has been recommended on at least one occasion by the National Transportation Safety Board). And while height and various weights 12 are also appropriate attributes for aircraft, birth date is not (date of manufacture or date of entry into ser- vice are however likely to be required). Furthermore, none of these is an appropriate attribute for cities. Attribute fact types enable the organization to identify which attribute terms are appropriate to which entity class (or object class) terms. For example, the following fact types capture some of the above discussion: F16. F17. F18. F19. F20. F21. F22. age is of person date of birth is of person height is of person weight is of person height is of aircraft model date of manufacture is of aircraft model date of entry into service is of aircraft model Attribute fact types are discussed in detail in Section 6.3.1.3. 6.1.11 Categorization schemes and categories