Explain why this project fails
Winburg Mini Case Study
Explain why this project fails
To reduce traffic congestion in downtown Winburg, Indiana, the mayor convinces the city to
set up a public transportation system. Bus-only lanes are to be established, and commuters
will be encouraged to “park and ride”; that is, to park their cars in suburban parking lots and
then take buses from there to work and back at cost of one dollar per ride. Each bus is to
have a fare machine that accepts only one dollar bills. Passengers insert a bill into the slots
as they enter the bus. Sensors inside the fare machine scan the bill, and the software in the
machine uses an image recognition
inserted a valid dollar bill into the slot. It is important that the fare machine be accurate
because, once the news gets out that any piece of paper will do the trick, fare income will
plummet to effectively zero. Conversely, if the machine regularly rejects valid dollar bills,
passengers will be reluctant to use the buses. In addition, the fare machine must be rapid.
Passengers will be equally reluctant to use the buses if the machine spends 15 seconds
coming to a decision regarding the validity of a dollar bill –it would take even a relatively
small number of passengers many minutes to board a bus. Therefore, the requirements for
the fare machine software include an average response time of less than 1 second, and an
average accuracy of at least 98 percent.
Episode 1 The first version of the software is implemented.
Episode 2 Test show that the required constraint of an average response time of 1 second
for deciding on the validity of a dollar bill is not achieved. In fact, on average, it takes 10
seconds to get a response. Senior management discovers the cause. It seems that, to get
the required 98 percent accuracy, a programmer has been instructed by her manager to use
double-precision numbers for all mathematical calculations. As a result, every operation
takes at least twice as long as it would with the usual single-precision numbers. The result is
that the program is much slower than it should be, resulting in the long response time.
Calculations then show that, despite what the manager told the programmer, the stipulated
98 percent accuracy can be attained even if single-precision numbers are used. The
programmer starts to make the necessary changes to the implementation.
Episode 3 Before the programmer can complete her work, further tests of the system show
that, even if the indicated changes to the implementation were made, the system would
still have an average response time of over 4.5 seconds, nowhere near the stipulated 1
second. The problem is the complex image recognition algorithm. Fortunately, a faster
algorithm has just been discovered, so the fare machine software is redesigned and rewritten
using the new algorithm. This results in the average response time being successfully
achieved.
เอกสารประกอบการสอน วิชา Princ of Software Development โดย ดร.ณัฏฐ์ดิษเจริญ
Episode 4 By now, the project is considerably behind schedule and way over budget. The
mayor, a successful entrepreneur, has the bright idea of asking the software development
team to try to increase the accuracy of the dollar bill recognition component of the system
as much as possible, to sell the resulting package to vending machine companies. To meet
this new requirement, a new design is adopted that improves the average accuracy to over
99.5 percent. Management decides to install that version of the software in the fare
machines. At this point, development of the software is complete. The city is later able to
sell its system to small vending machine companies, defraying about one-third of the cost
overrun.
Epilogue A few years later, the sensors inside the fare machine become obsolete and need
to be replaced by a newer model. Management suggests taking advantage of the change to
upgrade the hardware at the same time. The software professionals point out that changing
the hardware means that new software also is needed. They suggest rewriting the software
in a different
schedule and 25 percent over budget. However, everyone involved is confident that the
new system will be more reliable and of higher quality, despite “minor discrepancies” in
meeting its response time and accuracy requirements.
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