1. Notes on Software Quality
CS 425 Software Engineering
Notes on Software Quality
Sergiu Dascalu
University of Nevada, Reno
Department of Computer Science and Engineering

2. CS 425 Software Engineering
Overview
Software quality
Software quality assurance (SQA)
SQA challenges
Current trends
Research directions
Main references
CS 425 Software Engineering

3. CS 425 Software Engineering
1 Software Quality
It is rather hard to define what exactly software quality is
In general, it is acknowledged that software that satisfies its requirements has good quality
Several quality model exists, one of them stresses [Sommerville, 2006]:
Maintenability
Efficiency
Dependability
Acessibility
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4. CS 425 Software Engineering
1 Software Quality
In practical terms, software quality is important because lack of quality translates to user frustration, financial losses, material damages, human injuries and even deaths
Known disasters due to software failures include [Glass 1998; Endres and Rombach 2003]:
The baggage handling system for the Denver airport
The welfare administration system for the state of Florida
The air-traffic control system for the FAA
Other examples are listed by Tywebb Ltd
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5. CS 425 Software Engineering
1 Software Quality
Some other illustrations [YouTube 2008]:
Operating system demo crash
TV show software error
Arctic Tortoise field test problems
Autonomous crash in DARPA Urban Challenge
To do justice to software developers, their job is a very demanding one, something captured in the ad “if programmers had to make a plane” [YouTube 2008]
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6. CS 425 Software Engineering
2 Software Quality Assurance
Software Quality Assurance (SQA) is defined by the IEEE Standard – 1990 as “a planned and systematic pattern of all actions necessary to provide adequate confidence that an item or product conforms with established technical requirements”
The SQA Handbook defines SQA as “the set of systematic activities providing evidence of the ability of the software process to produce a software product that is fit to use” [Schulmeyer and McManus 1998]
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7. CS 425 Software Engineering
2 Software Quality Assurance
SQA is distinct from software quality control which consists primarily of inspecting requirements documents and software testing. SQA covers the entire software development process, which includes software specification, design, implementation, integration, testing, source code control, code reviews, version control, and release management [Wikipedia 2008].
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8. CS 425 Software Engineering
2 Software Quality Assurance
Also according to [Wikipedia 2008] SQA focuses on the control of processes, rather than on the control of products.
Current software processes have evolved for waterfall to the Unified Process (UP), with many variations in between
The waterfall model [Sommerville 2006]
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9. CS 425 Software Engineering
2 Software Quality Assurance
The Unified Process [Arlow and Neustadt 2005] 
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10. CS 425 Software Engineering
3 SQA Challenges
SQA challenges include [Voas 2003, Pressman 2004, McConnell 1993]:
Dealing with increasing complexity of software processes and products
Defining improved quality models
Integrating better with development processes
Increasing the evidence that standards that promote higher quality software bring indeed significant benefits
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11. CS 425 Software Engineering
3 SQA Challenges
SQA challenges include [Voas 2003, Pressman 2004, McConnell 1993] – continued:
Finding out ways to compose standards
Improving QA models and processes
Increasing software quality-centric adaptability
Increasing SQA independence from software development
Dealing with the perception that QA is less glamorous than development
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12. CS 425 Software Engineering
4 Current Trends
Current SQA trends relate to focusing on the following [Lyu 2007; SEI 2008; McConnell 1993; Sommerville 2006]:
Metrics and measurements
Methods and tools
Testing effectiveness and code coverage
Inspections, reviews, and walkthroughs
Software architectures
Management and certification
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13. CS 425 Software Engineering
5 Research Directions
Research directions in SQA, besides facing challenges mentioned previously, include [Lyu 2007; Bertolino 2007, Mnkandla 2006, Parsons 2003] :
QA for COTS-based software
QA for agile development processes
QA for open-source software
Metrics for software reliability prediction
100% automatic testing
Personal and Team software processes
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14. CS 425 Software Engineering
Main References
Endres, A and Rombach, D., A Handbook of Software and Systems Engineering, Addison-Wesley Pearson, 2003
Ghezzi, C., Jazayeri, M, and Mandrioli, D., Fundamentals of Software Engineering, 2nd edition, Prentice Hall, 2002.
McConnell, S., Code Complete: A Practical Handbook of Software Construction, Microsoft Press, 1993.
Pressman, R., Software Engineering: A Practitioner’s Approach, 6th edition, Prentice Hall, 2006.
Software Engineering Institute at Carnegie Melon University, last accessed March 8, 2008 at
Sommerville, I., Software Engineering, 8th edition, Addison-Wesley, 2006
Voas, J., Assuring Software Quality Assurance, IEEE Software, May?June 2003, pp
Wikipedia.com, last accessed March 9, 2008 at
YouTube.com, last accessed March 9, 2008 at
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