Modern Software Problems - The Technical and Social History of Software Engineering - page 361

Lessons learned: There are two lessons from this problem. One is obvious: Be
sure that all mathematical operations work as they should prior to release.
The second lesson is that when a vendor makes an error, don't put the burden
of proof on the consumer if you value your reputation and want to be considered
an ethical company.
Problem avoidance: This problem would have been found by inspections. It is
not likely to have been found by static analysis or requirements modeling. Pair
programming probably would not have been used, nor would it have found the
problem.
Why was the problem not found by testing? A possible reason is combinatorial
complexity. A chip with as many circuits, transistors, and features as the Pentium
might require close to an infinite number of test cases to find everything.
1993: Denver Airport Delays
As originally planned, the new Denver airport was supposed to have a state-of-the-
art luggage-handling system that would be almost fully computerized and directed
by software. What actually happened has become a classic story of a major soft-
ware failure with huge costs and delays.
Overall, the software and hardware problems with the luggage system delayed
the opening of the airport by about 16 months and cost about $560 million. This is
one of the few software topics that became a feature article in Scientific American .
A cut-down version of the original luggage-handling design was finally oper-
ational and ran for about five years. However, the costs exceeded the value, and
eventually it was replaced by a conventional luggage system.
The problems associated with the Denver airport luggage system are a litany of
common problems found with large software applications:
• Optimistic cost and schedule estimates
• Underestimating bugs and defects
• No formal risk analysis
• Excessive and poorly handled requirements changes
• Inadequate quality control, lacking inspections and static analysis
• Poorly designed test cases
• Serious gaps in testing
• Progress reports that concealed major problems