TABLE OF CONTENTS The Entity-Relationship (ER) modeling approach views an application domain in terms of entities that have attributes and participate in relationships. For example, the fact that an employee was born on a date is modeled by assigning a birth date attribute to the Employee entity type, whereas the fact that an employee works for a department is modeled as a relationship between them. This view of the world is quite intuitive, and in spite of the recent rise of UML for modeling object-oriented applications, ER is still the most popular data modeling approach for database applications.
In Chapter 1, I argued that ORM is better than ER for conceptual analysis. However, ER is widely used, and its diagrams are good for compact summaries, so you should become familiar with at least some of the mainstream ER notations. This is the main purpose of this chapter. A second purpose is to have a closer look at how ORM compares to ER. To save some explanation, I m going to assume you have already studied the basics of ORM in earlier chapters, so that we can examine ER from an ORM perspective.
The ER approach was originally proposed by Dr. Peter Chen in the very first issue of an influential journal (Chen 1976). Figure 8.1 is based on examples from this journal paper. Chen s original notation uses rectangles for entity types and diamonds for relationships (binary or longer). Attributes may be defined, but are excluded from the ER diagram. As...
