(Last modified Mon May 12 09:02 2008)
hw2 — Planning for quality
98 pts in all
-
8 pts total
Boehm and Ross's "Top Ten SRIs"
and the various lists of ilities
do not appear to have any overlap, and hardly even any connection.
4:
Does this mean that none of the ilities
is likely to cause trouble for a project?
Discuss (one paragraph).
In your discussion,
state a claim and
4:
support it with an argument.
-
40 pts total (8 pts per failure)
Give each of the
five well-known failures
(1-5)
an appropriate level of
2:
seriousness and
2:
cost,
from the eight
qualitative levels of seriousness (1-8)
and six qualitative levels of cost (a-f).
2 each:
Justify
each level of
seriousness and
cost
you choose
with an argument showing why it is more appropriate
than any other level.
If more than one level is plausible,
choose the one for which you can make the best argument;
as part of your argument,
show why your choice is better than the other plausible ones,
even if only somewhat better.
- Space shuttle non-launch
- $24 billion overdraft
- SDI
- Therac-25
- Phone switch
-
30 pts total (10 pts per risk)
Below are three risks with estimates of damage and probability.
Discuss each risk's
qualitative seriousness and cost levels,
dollar figure for damages, and probability,
giving arguments in support of what you claim.
Address each of these concerns:
-
2:
Are the statements plausible? Why or why not?
For example,
how many elevators at what cost would have to not be sold
to lose $100 million in sales,
and why or why not do you believe
a company might have sold that many?
Is $1 million a plausible cost
for developing elevator control software
(see the
cost statistics handout).
-
2:
Are the statements consistent for each risk?
That is,
are the risks and damages stated
over the same basis (per system or all installed systems,
per the same time unit or over the system's lifetime) —
state how they are or are not.
-
2:
Is there enough information for you to determine
the total probability
(for all systems over lifetime of system)
of each risk?
If so, explain how.
If not, what is missing?
-
2:
Is there enough information to calculate total cost
(for all systems over lifetime of system)?
If so, explain how.
If not, what is missing?
-
2:
Is there enough information to calculate a
probability×damage product?
Why, or why not (what is missing or inconsistent)?
- Risk:
Elevator control software development project will not produce
a usable system within any reasonable amount of time.
Seriousness level: n/a.
Cost level: n/a.
Damage: $100 million in lost sales,
$1 million in wasted development cost.
Probability of each occurrence: 30%.
- Risk:
"Blue screen" and reboot for system running the elevator control software
will occasionally immobilize all elevators in a building
for two to four minutes.
Seriousness level:
(2) "Essential organizational function blocked, no alternative.
Cost level: (b) "Damages for business losses".
Damage: $500 million in damages paid to building owners,
$10,000 to replace operating system for each installed system,
$200,000 to port control software to new operating system.
Probability of each occurrence: 15%.
- Risk:
In case of a cable or motor failure, the emergency braking system
will take long enough to go into action that passengers
may be injured.
Seriousness level: (1) "Human life endangered, injury possible".
Cost level: (a) "Suit for loss of life".
Damage:
A total of $15 million in damages paid to injured passengers
in each incident.
Probability of each occurrence: 2% probability
for a specific elevator over its expected 25 year lifetime.
-
12 pts total
You are an expert reviewer in charge of the reviewing of
your team's elevator goals, requirements, scenarios, and QA plan.
-
4:
What goals do you hope to achieve by doing this review
or sequence of reviews?
(List them.)
-
4:
Who do you want on the review team and why?
(List what kinds of reviewers
and give the expected benefits for each group.)
-
4:
What will you do in preparation for this review,
during the review itself, and afterwards?
(List the things.)
-
8 pts total
2:
Why does doing more-intensive QA reduce the total cost
of removing the same number of defects?
4:
Make a convincing argument supporting this claim,
being sure to include any rebuttals
that limit the extent to which it is true
or the conditions under which it is true.
2:
Illustrate your argument using
the tables in the QA Planning page.
