Web Database Applications with PHP and MySQL, 2nd Edition

Entity-Relationship Modeling

Entity-relationship (ER) modeling is a simple and clear method of expressing the design of database. ER modeling isn't new—it was first proposed by Chen in 1976—but it has emerged as the dominant modeling technique only in the past 15 years.

Figure E-2 shows a partial model of the winestore. In this diagram, you can see the relationship between a wine, a winery, and a wine-growing region. Each wine has attributes such as a wine_name, year, and a description. A wine is made by a winery, and each winery has a winery_name. Many wineries are located in a region, where a region has a region_name.

Figure E-2. A simple ER model showing the relationship between wines, wineries, and regions

ER diagrams aren't complicated, and we have already illustrated most of the features of ER modeling in Figure E-2. These features include:

Rectangles

Represent entities, the objects being modeled. Each entity is labeled.

Diamonds

Represent relationships between entities; a relationship is labeled with a descriptive title that explains how the entities interact.

Ellipses

Represent attributes that describe an entity. Underlined attributes are primary keys that uniquely identify instances of the entity.

Lines between rectangles and diamonds

Connect entities to relationships. Lines may be annotated, which means that the two ends can be marked with an M and an N, an M and a 1, an N and a ...