Software quality 1

Software quality factors

How to describe and measure software quality

Software quality 2

Quality in generalGarvin’s five definitions of quality (1988)

• Transcendent– Quality is universally recognizable

• Product-based– Quality is a precise and measureable variable

• User-based– Quality is fitness for intended use

• Manufacturing-based– Quality is conformance to specifications

• Value-based– Quality is defined in terms of costs and prices.

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The software life cycle

• The software life cycle describes the production, use, and maintenance of a piece of software.

• Different software has different life spans– Short life spans

• Prototypes made for an exhibition

– Long life cycles• Most administrative systems

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Functional vs. non-functional requirements

• Examples: Hotel reservation• Functional requirements

– Reservations and cancellations– Meals and extra services– Billings

• Non-functional requirements– Max. time to do reservation < 2 min– Downtime < 1%– Run on Microsoft Windows + Mac– Easy to change DBMS

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Software quality framework

• Software quality factor– Management-oriented view of produce quality

• Software quality criteria– Software-oriented attributes which provides

quality

• Software quality metrics– Quantitative measures of those attributes– Figure 1. Software quality framework, page

959

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Example quality factors

• Table 1. Example Quality Factors, page 959

• Figure 2. Quality factors perspectives, page 960

• Table 2. Definition of Software Quality Factors, page 961

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Definitions of software quality factors

• Figure 4. Relationship of criteria to software quality factors, page 963

• Table 4. Criteria Definitions for Software Quality Factors, page 965

• Figure 5. Relationships between software quality factors, page 967

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Grouping software quality factors

• Product operations– Will it work correctly now and in the future?

• Product revision– Can it be changed?

• Product transition– Can it be used in other contexts?– Figure 3. Allocation of software quality factors

to life cycle activity, page 962

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Metrics

• How to measure software quality?– We need some numbers!– Metrics are measurements of whether the criteria

exists or not, and to what degree

• Example metrics– Checklists: Grading the software– Inspection guidelines– Quantitative measures– Table 5. Quality Metrics Summary, page 966-967

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PracticeHow to do it?

• User quality goals• Identify quality requirements. Depends on

– Life cycle– Risk of use– Performance– Etc.– Figure 6. Quality factor specification process, page

968– Table 6. Quality Factors Relates to System

Characteristics, page 968

• Traceability

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References

• James McCall Quality Factors, page 958-969 in– John J. Marcianiak (editor) Encyclopedia of

Software Engineering, Volume 2, Wiley 1994

• David A. Garvin Managing Quality, The Free Press 1988, page 40-46