Hp Integrity NonStop J-Series Manuel d'utilisateur télécharger pdf (Page 237)

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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

Respfor

Figure 12-6. Relationships With New Class of Data

12-9

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Hp Integrity NonStop J-Series Manuel d'utilisateur Page 237

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