HP Integrity NonStop J-Series - Manual (Page 235)

Sample Project-Tracking System
Identifying Relationships Between Classes of Data
Identifying the Relationships Between Classes of Data
Identifying the relationship between classes of data helps to
isolate and solve problems of association between classes. To
identify the relationships, draw a diagram that shows each class
of data along with a brief explanation of connections between
them. Figure 12-4 shows such a diagram.
S5044-059
Projects Events
Employs
contain/define a
have managers/work on
are
assigned
to/work on
Figure 12-4. Relationships Between Classes of Data
After drawing the diagram, determine how many instances of one
class relate to instances of another. To illustrate, consider
the relationship between the "projects" data and the "employs"
data. Each project can have only one project manager.
Therefore, the relationship between these classes of data is
called one-to-one (abbreviated to 1:1).
The relationship between the "projects" data and the "events"
data is more complex. A project can have many events while an
event can have only one project. This type of relationship is
called a one-to-many relationship (in shorthand, 1:M).
12-7