1 Software Quality Concepts SWENET Module SQA 1

1 Software Quality Concepts SWENET Module SQA 1

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

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

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 (R. Glass) is a degree of excellence

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

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

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

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

9 Software Quality Attributes Product Revision Maintainability Flexibility Testability Product Transition Portability Reusability Interoperability Product Operation Correctness Integrity Reliability Usability Efficiency (Cavanno and Mc. Call, 1978)

Software Quality Attributes Boehm FURPS+ Usability Reliability Efficiency Usability Reliability Performance Functionality Supportability Portability Testability Understandability Modifiability Cavanno/Mc. Call Usability Reliability Efficiency Correctness Integrity Maintainability Portability Testability Flexibility Reusability Interoperability

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

Tradeoff Among Quality Attributes u Attributes – often conflict Ref Glass Portability Efficiency Usability Understandability

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