HP Integrity NonStop J-Series - Manual (Page 237)

Sample Project-Tracking System
Identifying Relationships Between Classes of Data
• In one-to-many relationships, data items that apply to both
classes can be included in the "one-occurrence" class to save
space in the files. The data items that identify unique
entries for the "one-occurrence" class can be included in
both--to provide a link between the classes.
To associate the "projects" and "events" data, include an item
within the "events" class that uniquely identifies a project,
such as "proj-code."
• All many-to-many relationships should be treated as a separate
class of data.
This rule offers a solution to the repeating data problem. If
you create a separate class of data that contains an
identifying item from "events" and an identifying item from
"employs," you can remove the repeating data (the employee
identification number) from "events."
Figure 12-6 shows a diagram that includes the new class of data.
S5044-061
Projects Events
Employs
1 M
1
1
M
M
1
Respfor
Figure 12-6. Relationships With New Class of Data
12-9