1. 1 Software Quality Concepts SWENET Module SQA1

2. Software Quality: Topics u Defining software quality u Attributes of software quality u Quality trade-offs u Quality attributes in requirements definition

3. Software Quality u What is quality? – In general – In business ?

4. Definitions: Quality is... u Quality is fitness for use (J. Juran) u Quality is the most profitable product line we have (H. Geneen) u Quality is free (P. Crosby) u Quality is compliance to a standard (W.E. Perry) u Quality is a degree of excellence (R. Glass)

5. Quality Concepts u Cost effective investment u Relative / Absolute – Within a Context? – Cadillac versus Chevrolet u Compared to some standard – Measurement and analysis implied u An intangible

6. Definition: Software Quality u What is software quality? u What are the attributes of quality for software? ? This is high quality software because...

7. Software Quality Attributes Portability Reliability Efficiency Usability Testability Understandability Modifiability (Boehm, 1978)

8. Software Quality Attributes FURPS+ Functionality Usability Reliability Performance Supportability ( Grady / Hewlett-Packard)

9. 9 Software Quality Attributes Product Revision Maintainability Flexibility Testability Product Transition Portability Reusability Interoperability Product Operation CorrectnessIntegrity ReliabilityUsability Efficiency (Cavanno and McCall, 1978)

10. Software Quality Attributes FURPS+Boehm Cavanno/McCall Reliability Usability PerformanceEfficiency Integrity FunctionalityCorrectness Supportability Portability Testability Understandability Modifiability Maintainability Portability Testability Flexibility Reusability Interoperability

11. 11 Trade-offs and Quality u Software engineers must make trade-offs on many levels and quality is no exception u Quality compromises include – Trade-off among quality attributes – Trade-off of quality for other factors Discussion: What trade-offs (including quality) might affect a choice to purchase one of the following: - Luxury sedan - Low end compact - Pick-up truck

12. Tradeoff Among Quality Attributes u Attributes often conflict – Ref Glass Portability EfficiencyUsability Understandability

13. Trade-off of Quality for Other Factors u Quality competes with other demands – Short term vs. long term effects Time Cost Quality