Database
A database can interconnect tables . Relationships between tables can be defined in the database to enforce integrity rules called constraints (rules that make sure connections between tables are valid). Three tables that are related to one another. An integrity rule for these tables would make sure that every CD in the INVENTORY table, for example, is connected to a CD in the CD table.
A database saves space by relating data rather than repeating data . For example, in Figure 3.2, the title, label, and artist are listed in the CD table. The CD_ID in the fifth row of the INVENTORY table is 100. By looking back at the CD table row for ID 100, you know that the CDRock store has 44 copies of “Soak Up The Sun” by Sheryl Crow on the A&M record label.