HP 3000 Manuals HP 3000 Manuals
From Entities to Tables
Once you have added the necessary key attributes that support
relationships, you have arrived at a set of relational tables: the
attributes are now columns, and the key values are now key columns. From
what has been done so far, you can see a set of relational tables
emerging, as follows ( * indicates a key column):
Columns and Keys for Four Tables
-------------------------------------------------------------------------------------------------
- Albums Table - Selections Table - Composers Table - Log Table -
-------------------------------------------------------------------------------------------------
- *AlbumCode - *AlbumCode - *ComposerName - *AlbumCode -
- AlbumTitle - *SelectionName - Birth - *SelectionName -
- Medium - ComposerName - Death - StartTime -
- AlbumCost - Timing - Birthplace - EndTime -
- RecordingCo - Performers - Comment - Announcer -
- DateRecorded - - - -
- MfgCode - - - -
- Comment - - - -
-------------------------------------------------------------------------------------------------
Note that the Selections and Log tables each have two key columns,
whereas the other tables have only one apiece. Remember that a key must
uniquely identify each entry in the table.