HP Integrity NonStop J-Series - Manual (Page 238)

Sample Project-Tracking System
Listing Fields in Each File
At this point, you have identified the files that you need for
the project-tracking system. Each data class ("projects,"
"events," "employs," and now "respfor") corresponds to a file.
Listing the Fields in Each File
Having identified the files, you can list the fields in each.
Figure 12-7 lists the fields in the files used by the
project-tracking system.
-----------------------------------------------------------------
| |
| File Fields |
|_______________________________________________________________|
| |
| Projects proj-code, proj-desc, proj-status, |
| proj-start-date, proj-end-date, proj-mgr |
| |
| Events proj-code, event-num, event-desc, |
| predict-start-date, predict-end-date, |
| revised-start-date, revised-end-date, |
| change-info, update-emp |
| |
| Respfor proj-code, event-num, emp-no |
| |
| Employs emp-no, emp-name, dept-name |
| |
-----------------------------------------------------------------
Figure 12-7. List of Fields in Each File
Notice that fields such as "proj-code," "event-num," and "emp-no"
appear in a number of files. This duplication of fields is
essential to link the files for a multifile application.
Identifying Key Fields
A primary key field is any field with a value that uniquely
identifies a record. In the projects file, for example, there
can be only one record for each "proj-code." Thus, "proj-code"
can be the primary key for the "projects" file. Similarly, an
"emp-no" uniquely identifies a record in the "employs" file.
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