Code Complete, 2nd Edition

Indexed Access Tables

Sometimes a simple mathematical transformation isn't powerful enough to make the jump from data like Age to a table key. Some such cases are suited to the use of an indexed access scheme.

When you use indexes, you use the primary data to look up a key in an index table and then you use the value from the index table to look up the main data you're interested in.

Suppose you run a warehouse and have an inventory of about 100 items. Suppose further that each item has a four-digit part number that ranges from 0000 through 9999. In this case, if you want to use the part number to key directly into a table that describes some aspect of each item, you set up an index array with 10,000 entries (from 0 through 9999). The array is empty ...