
many:many relationship may, in general, include 1:many (in either direction), 1:1, 1:0
and 0:1 relationships, although some, or all, of these possibilities could be excluded
from a many:many relationship by more restrictive enterprise rules.
Notation
Figure 9.2 shows how the degree of a relationship is represented on an entity-
relationship type diagram. Answers to questions which ask for an entity-relationship
type diagram should always show the degree of each relationship if the information is
available.
Fig. 9.2 Representation of relationship degree on an entity-relationship type diagram
(a) Representation of 1:1 relationship
(b) Representation of ...