Database Modeling and Design - Database Systems - page 81

In order to unify the informal E-R model with the formal relational model, Codd
introduced a number of conventions specific to the E-R model. These are summarized
in Figure 5-1 and illustrated in Figure 5-2 . Note that the model displayed in the figure
represents only a section of the (partial) database model introduced in chapter 3
(review Figure 3-4b). Figure 5-2a employs the Chen notation, while Figure 5-2b employs
the Crow's Foot notation. In both cases, the attributes of entities have been omitted,
except for primary key attributes (as mentioned in chapter 3 and emphasized later in this
chapter, there are more creative ways to represent attributes). Figure 5-3 illustrates the
representation of super-type and subtype relationships.
Figure 5-1. E-R Model Conventions