Data Modeling with the Entity-Relationship Model - Database Processing: Fundamentals, Design, and Implementation - page 194

two and possibly many salespeople. Sometimes, when no appropriate form or report exists,
teams create a prototype form or report for the users to evaluate.
All of this means that you must understand how the structure of forms and reports deter-
mines the structure of the data model and the reverse. Fortunately, many forms and reports
fall into common patterns. If you learn how to analyze these patterns, you will be well on your
way to understanding the logical relationship between forms and reports and the data model.
Accordingly, in the next sections, we will discuss the most common patterns in detail.

Strong Entity Patterns
Three relationships are possible between two strong entities: 1:1, 1:N, and N:M. When model-
ing such relationships, you must determine both the maximum and minimum cardinality.
The maximum cardinality often can be determined from forms and reports. In most cases, to
determine the minimum cardinality, you will have to ask the users.

1:1 Strong Entity Relationships
Figure 5-15 shows a data entry form and a report that indicate a one-to-one relationship between
the entities CLUB_MEMBER and LOCKER. The Club Member Locker form in Figure 5-15(a)
shows data for an athletic club member, and it lists just one locker for that member. This form
indicates that a club member has at most one locker. The report in Figure 5-15(b) shows the
lockers in the club and indicates the member who has been allocated that locker. Each locker is
assigned to one club member.
The form and report in Figure 5-15 thus suggest that a CLUB_MEMBER has one LOCKER
and a LOCKER is assigned to one CLUB_MEMBER. Hence, the relationship between them is
1:1. To model that relationship, we draw a nonidentifying relationship (meaning the relation-
ship is strong and not ID-dependent) between the two entities, as shown in Figure 5-16. We
then set the maximum cardinality to 1:1. You can tell that this is a nonidentifying relationship

(a) Club Membership Data Entry Form

Figure 5-15
Form and Report Indicating
a 1:1 Relationship

(b) Club Locker Report