Mapping Cardinalities

The ternary relationship of Figure 2.13 could be replaced by a pair of binary relationships, as shown in Figure 2.22.

  
Figure 2.22: Representation of Figure 2.13 using binary relationships

However, there is a distinction between the two representations:

• In Figure 2.13, relationship between a customer and account can be made only if there is a corresponding branch.
• In Figure 2.22, an account can be related to either a customer or a branch alone.

• The design of figure 2.13 is more appropriate, as in the banking world we expect to have an account relate to both a customer and a branch.