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ECE 322
SOFTWARE TESTING AND MAINTENANCE
Assignment #1

(return to the appropriate section’s box- ECE 322 – 2nd floor DICE building)
Total: 40 points
Value 10 points
Please be concise.
1.Study two papers entitled (located in the Readings folder)
No silver bullet published in IEEE Computer
The software engineering silver bullet conundrum published in IEEE Software
Based on this material, what are, in your opinion, the two most essential factors making software
testing activities difficult? Distinguish between technical and non-technical (say, organizational,
human, etc.) factors. Justify your opinion along with solid and convincing arguments.
Value 10 points
2.Consider a software system for an autonomous vehicle and in this context discuss the meaning
of the pertinent software qualities (say, functionality, reliability, portability, efficiency, etc.).
Name them and complete a quality risk analysis. Rate technical risks and business risks. Use a 5-
point scale (1- very high, 2- high… 5- very low).
Value 10 points
3. The software requirement specification document for the tender for the development of “superlab” software system for managing a hospital laboratory, consists of chapter headings that are in
accordance with the required quality factors. In the following table, there are sections from the
requirements document.
For each section below, fill in the name of the McCall factor that best fits the requirement (choose
only one factor per requirements section).
number Section taken from the software
requirement document
The quality factor
1 The probability that the “superlab” software will be found in a
state of failure during peak hours
(9AM to 4PM) is required to be
below 0.002.
2 The “super-lab” software will
enable the direct transfer of
laboratory results to those files of
hospitalized patients managed by
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MD software package
3 The training of laboratory
technician, requiring no more
than 3 days, will enable the
technician to reach level C of
“super-lab” operator. This means
that the trainee will be able to
manage the reception of 20
patients per hour.
4 The software system should be
able to serve 12 workstations and
8 automatic testing machines with
a single model AS20 server and
CS25 communication server that
will be able to serve 25
communication lines. The
hardware system should conform
to all availability requirements as
listed in Appendix D.
Value 10 points
4. Discuss another example (being different from those already covered in lecture notes) of
software failures. Do some Web search and literature review. Clearly identify a source of your
information (e.g., include a link to the website). Describe a nature of the software failure. Identify
its origin. Were there any software testing efforts mentioned in relation to the resulting failure?
Was there any follow up action taken? Was there any plan to alleviate further problems?
Be critical in your assessment – sometimes the quality of the available source of information
could be questionable (which is a typical downfall of many Web resources). Use at least two
different sources; they might offer various perspectives on the same problem. You may wish to
organize your findings in a tabular format. Offer the most essential info; be concise.
In your writing use the following template identifying failure description, nature of software
failure, testing efforts regarding failure, follow up action, and URL where the material was found.
This is a sample
Failure description Therac-25 Accidents
Eleven Therac-25s, radiation therapy machines, were installed: five in
the US and six in Canada. Six accidents involving massive overdoses
to patients occurred between 1985 and 1987.
The accidents occurred when the high-energy electron-beam was
activated without the target having been rotated into place; the
machine’s software did not detect that this had occurred, and did not
therefore determine that the patient was receiving a potentially lethal
dose of radiation, or prevent this from occurring. The very high
energy electron-beam directly struck the patients causing the feeling
of an intense electric shock and the occurrence of thermal and
radiation burns. In some cases, the injured patients died later from
radiation poisoning.
Nature of software failure Several features of the Therac-25 are important in understanding the
accidents. Some of essential causes were:
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(1) The engineers had reused software from older models. These
models had hardware interlocks that masked their software defects.
Those hardware safety mechanisms had no way of reporting that they
had been triggered, to at least indicate the existence of faulty software
commands
(2) The hardware provided no way for the software to verify that
sensors were working correctly
(3) The software was written in assembly language. While this was
more common at the time than it is today, assembly language is harder
to debug than most high-level languages.
Any testing efforts
regarding the failure?
(1) Related problems were found in the Therac-20 software. These
were not recognized until after the Therac-25 accidents because the
Therac-20 included hardware safety interlocks and thus no injuries
resulted.
(2) After the 2nd incident the Atomic Energy of Canada Limited
(AECL) sent a service technician to the Therac-25 machine. He was
unable to recreate the malfunction and therefore concluded that
nothing was wrong with the software. Some minor adjustments to the
hardware were made.
Any follow up action taken?
Any plan to alleviate further
problems?
The machine was recalled in 1987 and the AECL made a variety of
changes in the software of the Therac-25 radiation treatment system.
The machine itself is still in use today.
URL (1) http://en.wikipedia.org/wiki/Therac-25
(2) The Therac-25 Accidents (PDF):
http://sunnyday.mit.edu/papers/therac.pdf
(3) An Investigation of the Therac-25 Accidents (IEEE Computer)
http://courses.cs.vt.edu/~cs3604/lib/Therac_25/Therac_1.html

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