Question

A 12-lane toll plaza on a busy interstate highway has to deal with the thousands of EZ-Pass drivers passing through every hour. Drivers acquire pre-paid EZ-Pass cards from the toll plaza at levels of $50 and $100. [Currently, about 100,000 drivers hold pre-paid EZ-Pass cards.] Each EZ-Pass card has a unique 1-digital ID number. Every time an EZ-Pass driver passes through the toll plaza, a fixed amount of $2 (for 2-axle vehicles) or $5 (for all other vehicles) is deducted from the driver's prepaid account. Due to the heavy volume of traffic, the toll plaza has a fraction of a second to: a) capture the EZ-Pass ID of the driver, b) record the pass through, and c) deduct the driver's account.

Identify the critical attributes necessary to enable the toll plaza operations. How would you organize the attributes into tables?

Answer 1

There should be follwing tables:

EZ-Pass  table:
ID Pimary key,
Vehicle ID Foreign key References Vehicle,
Balance($).

Vehicle table:
Vehicle ID Primary key,
Deduction                                       ($2 or $5 per trip depending on no of axle)
ID Foreign key References EZ-Pass.

This organization of attributes is enough to support the operations of toll plaza.