SECTION II

Data Model Objects

This section explains all of the objects on a data model. By the end of this section, you will be able to “read” a data model of any size or complexity, as well as create and modify entities, attributes, and relationships in ER/Studio.

Chapter 4 defines an entity and instances and discusses the different categories of entities. The three different levels at which entities may exist, conceptual, logical, and physical, are also explained. Chapter 5 defines a submodel and how to work with submodels. Chapter 6 defines an attribute and defines keys, distinguishing the terms candidate, primary, surrogate, foreign, and alternate key. Domains are also introduced in this chapter. Chapter 7 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 also discussed.