The following figure shows the telephone directory example
and includes the entities, relationships, and attributes. This diagram
includes the relationships that you establish with the matrix. After
you study the diagram symbols, compare the E-R diagram in the following
figure with the matrix in ids_ddi_171.html#ids_ddi_171__sii-02-30139. Verify for
yourself that the relationships are the same in both figures.
A
matrix such as ids_ddi_171.html#ids_ddi_171__sii-02-30139 is
a useful tool when you first design your model, because when you fill
it out, you are forced to think of every possible relationship. However,
the same relationships appear in a diagram such as the following figure,
and this type of diagram might be easier to read when you review an
existing model. Figure 1: Preliminary
entity-relationship diagram of the telephone directory example