Software Engineering for Students A Programming Approach

SELF-TEST QUESTION
17.1 Categorize the following eventualities:
17.2 ● Fault detection by software
17.2 Fault detection by software 239
Clearly, the difference between anticipated and unanticipated faults is a rather arbitrary
distinction. A better terminology might be the words “exceptional circumstances”
and “catastrophic failures”. Whatever jargon we use, we shall see that the two
categories of failure are best dealt with by two different mechanisms.
Having identified the different types of faults, let us now look at what has to be done
when a fault occurs. In general, we have to do some or all of the following:
■ detect that a fault has occurred
■ assess the extent of the damage that has been caused
■ repair the damage
■ treat the cause of the fault.
As we shall see, different mechanisms deal with these tasks in different ways.
How serious a problem may become depends on the type of the computer application.
For example power failure may not be serious (though annoying) to the user of a
personal computer. But a power failure in a safety critical system is serious.
Faults can be prevented and detected during software development using the following
techniques:
■ good design
1. the system stack (used to hold temporary variables and method
return addresses) overflows
2. the system heap (used to store dynamic objects and data structures)
overflows
3. a program tries to refer to an object using the null pointer (a pointer
that points to no object)
4. the computer power fails
5. the user types a URL that does not obey the rules for valid URLs.
■ using structured walkthroughs
■ employing a compiler with good compile-time checking
■ testing systematically
■ run-time checking.