Home > Articles > Process Improvement

  • Print
  • + Share This
This chapter is from the book

This chapter is from the book

Defining Software Quality

Quality has always been a difficult topic to define, and software quality has been exceptionally difficult. The reason is that perceptions of quality vary from person to person and from object to object.

For software quality for a specific application, the perceptions of quality differ among clients, developers, users, managers, software quality personnel, testers, senior executives, and other stakeholders. The perceptions of quality also differ among quality consultants, academics, and litigation attorneys. Many definitions have been suggested over the years, but none have been totally satisfactory or totally adopted by the software industry, including those embodied in international standards.

The reason that quality in general and software quality in particular have been elusive and hard to pin down is because the word "quality" has many nuances and overtones. For example, among the attributes of quality can be found these ten:

  1. Elegance or beauty in the eye of the beholder
  2. Fitness of use for various purposes
  3. Satisfaction of user requirements, both explicit and implicit
  4. Freedom from defects, perhaps to Six Sigma levels
  5. High efficiency of defect removal activities
  6. High reliability when operating
  7. Ease of learning and ease of use
  8. Clarity of user guides and HELP materials
  9. Ease of access to customer support
  10. Rapid repairs of reported defects

To further complicate the definition, quality often depends on the context in which a software component or feature operates. The quality of a software component is not an intrinsic property—the exact same component can be of excellent quality or highly dangerous depending on the environment in which it operates or the intent of the user.

This contextual nature of software quality is a fundamental challenge and applies to each of the ten attributes just listed. What is elegant in one situation might be downright unworkable in another; what is highly reliable under certain conditions can quickly break down in others.

A closely related complication is what Brooks calls "changeability" of software. "In short, the software product is embedded in a cultural matrix of applications, users, laws, and machine vehicles. These all change continually, and their changes force change upon the software product." (Brooks 1995, p.185)

This brings us to the distinction between testing and software quality. Software quality is often loosely equated with the activities of testing or quality assurance. However, contextuality and Brooks' notion of changeability of software are the reasons why software quality cannot be equated with testing or quality assurance.

Testing can only tackle known unknowns. If you don't know what you're testing for, you are not, by definition, conducting tests. But software, by its very nature is subject to unknown unknowns. No amount of functional or nonfunctional testing can be designed to detect and correct these problems. For example, the behavior of the application can change when

  • One or more application components are switched out for new components
  • Components change for technology reasons (such as version upgrades)
  • Components change for business reasons (such as for new features or a change in workflow)
  • Or the application's environment (perhaps the technology stack, for example) changes

It is impossible to devise tests for these conditions in advance. However, from experience we know that some applications are more robust, reliable, and dependable than others when the environment around them changes. Some applications are much easier to modify or extend in response to pressing business needs. These attributes of an application—robustness, dependability, modifiability, and so on—are reliable indicators of application quality that go beyond the defects identified during testing or the process inefficiencies or compliance lapses indentified in quality assurance. Therefore, the quality of an application can and must be defined in such a way as to accommodate these indicators of quality that outrun those identified in testing and quality assurance. How the concepts of contextuality and changeability can be accounted for in defining and measuring software quality is addressed at length in Chapter 2.

There are seven criteria that should be applied to definitions of software quality in order to use the definition in a business environment for economic analysis:

  1. The quality definition should be predictable before projects start.
  2. The quality definition should be measurable during and after projects are finished.
  3. The quality definition should be provable if litigation occurs.
  4. The quality definition should be improvable over time.
  5. The quality definition should be flexible and encompass all deliverables.
  6. The quality definition should be extensible and cover all phases and activities.
  7. The quality definition should be expandable to meet new technologies such as cloud computing.

In addition, the various nuances of quality can be categorized into seven major focus areas or quality types:

  1. Technical or Structural quality, which includes reliability, defects, and defect repairs
  2. Process quality, which includes development methods that elevate quality
  3. Usage quality, which includes ease of use and ease of learning
  4. Service quality, which includes access to support personnel
  5. Aesthetic quality, which includes user satisfaction and subjective topics
  6. Standards quality, which includes factors from various international standards
  7. Legal quality, which includes claims made in lawsuits for poor quality

The reason that taxonomy of quality types is needed is because the full set of all possible quality attributes encompasses more than 100 different topics. Table 1.5 lists a total of 121 software quality attributes and ranks them in order of importance.

Table 1.5. Seven Types of Software Quality Factors

Quality Factors

Value

Technical Quality Factors

1

Few requirements defects

10.00

2

No toxic requirements

10.00

3

Zero error-prone modules

10.00

4

Low defect potentials

10.00

5

Use of certified reusable code

10.00

6

Low rates of severity 1 and 2 defects

10.00

7

High reliability

9.90

8

Strong security features

9.90

9

Few design defects

9.50

10

Few coding defects

9.50

11

Low bad-fix injection rate

9.50

12

Low rates of invalid defect reports

9.50

13

Low rates of legacy defects

9.50

14

Easy conversion to SaaS format

9.00

15

Easy conversion to Cloud format

9.00

16

Fault tolerance

8.00

17

Few defects in test cases

8.00

18

Low cyclomatic complexity

7.50

19

Low entropy

7.00

Process Quality Factors

20

Customer support of high quality

10.00

21

High defect detection efficiency (DDE)

10.00

22

High defect removal efficiency (DRE)

10.00

23

Accurate defect measurements

10.00

24

Use of formal defect tracking

10.00

25

Accurate defect estimates

10.00

26

Low total cost of ownership (TCO)

10.00

27

Executive support of quality

10.00

28

Team support of quality

10.00

29

Management support of quality

10.00

30

Accurate quality benchmarks

10.00

31

Effective quality metrics

10.00

32

Minimizing hazards of poor quality

10.00

33

Use of formal quality improvement plan

10.00

34

COQ: appraisal

10.00

35

COQ: prevention

10.00

36

COQ: internal failure

10.00

37

COQ: external failure

10.00

38

Cost of learning (COL)

10.00

39

Quality improvement baselines

9.90

40

Function point quality measures

9.80

41

Quality and schedules

9.00

42

Quality and costs

9.00

43

Use of formal inspections

9.00

44

Use of automated static analysis

9.00

45

Use of formal test case design

9.00

46

Use of reusable test data

9.00

47

Use of formal SQA team

9.00

48

Use of trained test personnel

9.00

49

Use of formal test library controls

9.00

50

Use of formal change management

9.00

51

Use of Six Sigma for software

9.00

52

Use of Team Software Process (TSP)

9.00

53

Use of Agile methods

9.00

54

Use of Rational methods (RUP)

9.00

55

Use of hybrid methods

9.00

56

Use of Quality Function Deployment (QFD)

9.00

57

Use of trained inspection teams

9.00

58

Use of CMMI levels = > 3

9.00

59

Use of legacy renovation tools

9.00

60

Low rates of false-positive defects

9.00

61

Low rates of duplicate defect reports

8.75

62

Use of refactoring and restructuring

8.50

63

Six-Sigma quality measures

8.50

64

High test coverage

8.00

65

Low Cost of Quality (COQ)

8.00

66

Use of automated test tools

8.00

67

Use of story point quality metrics

2.00

68

Use of Use Case point quality metrics

2.00

69

Use of waterfall methods

1.00

70

Lines of code quality measures

-5.00

71

Use of CMMI levels = < 2

-5.00

72

Cost-per-defect quality measures

-7.00

73

Executive indifference to high quality

-10.00

74

Management indifference to high quality

-10.00

75

Team indifference to high quality

-10.00

76

Customer indifference to high quality

-10.00

Usage Quality Factors

77

Ease of use

10.00

78

Useful features

10.00

79

Ease of learning

10.00

80

Good tutorial manuals

10.00

81

Good training courses

10.00

82

Good on-line HELP

10.00

83

Useful HELP information

9.75

84

Defect repair costs

9.25

85

Low cost of learning (COL)

9.25

86

User error handling

9.00

87

Speed of loading

9.00

88

Speed of usage

9.00

89

Good nationalization for global products

9.00

90

Documentation defects

9.00

91

Easy export of data to other software

9.00

92

Easy import of data from other software

9.00

93

Useful manuals and training

8.50

94

Good assistance from live experts

Service Quality Factors

95

Good customer service

9.50

96

Rapid defect repair speed

9.25

97

Good technical support

9.00

98

Good HELP desk support

9.00

99

Use of formal incident management

8.00

100

Use of ITIL policies

8.00

Aesthetic Quality Factors

101

High user satisfaction

10.00

102

Superior to competitive applications

10.00

103

Superior to legacy applications

10.00

104

Quick start-up and shut-down times

9.00

105

No feature bloat

7.00

Standards Quality Factors

106

ISO/IEEE standards compliance

10.00

107

Certification of reusable materials

10.00

108

Corporation standards compliance

10.00

109

Certification of test personnel

8.00

110

Certification of SQA personnel

8.00

111

Portability

7.00

112

Maintainability

6.00

113

Scalability

5.00

Legal Quality Factors

114

Good warranty

10.00

115

Partial warranty: replacement only

4.00

116

Litigation for poor quality—consequential

-10.00

117

Litigation for poor quality—contractual

-10.00

118

Litigation for poor quality—financial loss

-10.00

119

Litigation for poor quality—safety

-10.00

120

Litigation for poor quality—medical

-10.00

121

No warranty expressed or implied

-10.00

The ranking scheme ranges from +10 for topics that have proven to be extremely valuable to a low of -10 for topics that have demonstrated extreme harm to software projects.

A total of 121 quality factors is far too cumbersome to be useful for day-to-day quality analysis. Table 1.6 lists the top 12 quality factors if you select only the most significant factors in achieving quality based on measurements of several thousand applications.

Table 1.6. The 12 Most Effective Software Quality Factors

1. Low defect potentials

2. Effective defect prevention methods

3. High defect detection efficiency (DDE)

4. High defect removal efficiency (DRE)

5. Use of pretest inspections

6. Use of pretest static analysis

7. Use of formal test case design

8. Good ease of learning

9. Good ease of use

10. Good technical support

11. High user satisfaction

12. Good warranty

As of 2011, 11 of these 12 quality factors are technically achievable. Item 114 on the list, Good warranty, is not yet practiced by the software industry. This situation needs to change, and the software industry needs to stand behind software applications with effective warranty coverage.

Though all 121 of the quality factors are important, in order to deal with the economic value of quality, it is obvious that the factors have to be capable of quantitative expression. It is also obvious that the factors have to influence these seven topics:

  1. The costs of development, maintenance, enhancement, and support.
  2. The schedules for development, maintenance, enhancement, and support.
  3. The direct revenue that the application will accrue if it is marketed.
  4. The indirect revenue that might accrue from services or related products.
  5. The learning curve for users of the application.
  6. The operational cost savings that the application will provide to users.
  7. The new kinds of business opportunities that the application will provide to users.

This book concentrates on software quality factors that have a tangible impact on costs and revenue. And to deal with the economic value of these quality factors, the book addresses three critical topics:

  • What are the results of "average quality" in terms of costs, schedules, revenue, and other financial topics? Once defined, average quality will provide the baseline against which economic value can be measured.
  • What are the results of "high quality" in terms of cost reduction, schedule reduction, higher revenues, new market opportunities, and other financial topics?
  • What are the consequences of "low quality" in terms of cost increases, schedule increases, reduced revenue, loss of customers, and other financial topics?

Usually, more insights result from polar opposites than from average values. Therefore the book concentrates on the economic value from high quality and the economic losses from low quality.

While average quality is important, it is not very good, nor has it ever been very good for software. Therefore, it is important to know that only better-than-average software quality has tangible economic values associated with it.

Conversely, low software quality brings with it some serious economic consequences, including the threat of class-action litigation, the threat of breach of contract litigation, and, for embedded software in medical devices, even the potential threat of criminal charges.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020