166 CHAPTER 7 How to write quality natural language rule statements 7.2.3.2 Subjects of data rule statements For each type of data rule statement, there are restrictions on what term can be the subject of that rule statement: 1. for a data cardinality rule statement, the term signifying the transaction (form or message) or persis- tent data record in which a data item is required or prohibited (see Section 7.2.3.2.1 for more details); 2. for a data content rule statement, the term signifying the data item, combination of data items, or set of data items for which the content is constrained (see Section 7.2.3.2.2 for more details); 3. for a data update prohibition rule statement that specifies a non-transferable relationship, the term signifying the record for which a relationship cannot be transferred; 4. for any other data update rule statement, either a. the term signifying the data item for which update is prohibited or restricted, or b. the term `data item' if all data items for a particular transaction or record are prohibited from update. 7.2.3.2.1 Subjects of data cardinality rule statements The subject of any data cardinality rule statement (except one for a dependent cardinality rule) must be the term signifying the transaction or persistent data record in which a data item is required or prohibited. Each type of incoming form (paper or on-screen) should be assigned an agreed term (often one that