4.9 A complete taxonomy of rules 85 3. If the rule is concerned only with the presence or absence of one or more data items, how many instances of a data item there are, or the content of one or more data items, the rule is a data rule. 4. If none of the above, the rule is an activity rule. 4.9.1 Definitional rules Definitional rules can in turn be categorized as 1. formal term definitions, which define business terms formally: a. formal intensional definitions (described in Section 4.9.1.1.1) b. formal extensional definitions (described in Section 4.9.1.1.2) c. symbolic literal definitions (described in Section 4.9.1.1.3); 2. categorization scheme enumerations, which define members of categorization schemes (described in Section 4.9.1.2); 3. category transition constraints, which define constraints on the transitions between categories in a categorization scheme (described in Section 4.9.1.3); 4. complex concept structure rules, which define constraints on the components of complex concepts: a. complex concept cardinality rules (described in Section 4.9.1.4.1) b. complex concept equivalence rules (described in Section 4.9.1.4.2)