SECTION II

Data Model Components

Section II explains all of the symbols and text on a data model. It contains the next five chapters, four of which describe different components of the data model. The remaining chapter describes the importance of quality names and definitions. By the time you finish this section, you will be able to ‘read’ a data model of any size or complexity.

Chapter 3 defines an entity and discusses the different categories of entities. Entity instances are also defined. The three different levels at which entities may exist, subject area, logical, and physical, are also explained, as well as the concepts of weak versus strong entities.

Chapter 4 defines a data element and discusses domains. Examples are provided for the three different types of domains.

Chapter 5 defines rules and relationships. Data rules are distinguished from action rules. Cardinality and labels are explained so that the reader can read any data model as easily as reading a book. Other types of relationships, such as recursive relationships, and subtyping are discussed, as well.

Chapter 6 expands on the statement that “Data can only be used effectively if it can be understood, and it can only be understood if the definitions are adequate”, by focusing on the characteristics of definitions - clarity, completeness, accuracy, and lack of ambiguity.

Chapter 7 defines keys and distinguishes the terms candidate, primary, and alternate key. Surrogate keys and foreign keys are also defined, along with a discussion on their importance.