Picture yourself at your desk keeping track of your household income and expenses in a proper-based ledger. The process entails adding up and keeping track of multiple pieces of information: paychecks and other kinds of income; grocery expenses, automobile expenses, medial expenses, debt service, and so on. You'd keep each of these running totals in a separate column, and later you'd probably add them all up to create a view into your financial situation. If you were writing a computer program to keep up with all this information instead of using your paper-based ledger, you would probably store the permanent data in a database, but while your program was accepting input of the numbers and keeping track of the totals, it would use different variables to keep up with each different piece of information.
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