Assignment #1 Solution

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 “super-
lab” 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   The quality factor

requirement document
1
The  probability  that  the  “super-

lab” 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
Therac-25 Accidents
Failure description


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
Nature of software failure
radiation poisoning.

Several features of the Therac-25 are important in understanding the

accidents. Some of essential causes were:

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Any testing efforts regarding the failure?








Any follow up action taken? Any plan to alleviate further problems?

URL

    (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.


    (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.

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.


    (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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