HP Integrity NonStop J-Series - Manual (Page 236)

Sample Project-Tracking System
Identifying Relationships Between Classes of Data
The relationship between the "events" data and the "employs" data
is even more complex. An event can have many employees and an
employee can have many events. Thus, the relationship between
these two classes of data is many-to-many (or M:M).
Figure 12-5 shows a diagram of these relationships.
S5044-060
Projects Events
Employs
1 M
1
1
M
M
Figure 12-5. Relationships Between Instances of Classes of Data
To summarize, the relationships shown in Figure 12-5 are:
One project has one manager 1:1
One project has many events 1:M Each event has one
project
One event can have many employees M:M One employee can
have many events
Depending upon the type of relationship, the following rules may
apply:
• With the exception of items involved in more than one
relationship, data items that belong to classes with a
one-to-one relationship can often be merged into a single
class. Since the "employs" data is also related to the
"events" class, the "projects" and "employs" data should not
be merged.
12-8