【正文】 軟體品質(zhì)管理 Introduction ? What is software quality? ? How can it be measured? – How can it be measured before the software is delivered? ? Some key quality factors ? Some measurable indicators of software quality Introduction ? Think of an everyday object – . a chair – How would you measure it’ s “ quality” ? ? construction quality? (. strength of the joints,…) ? aesthetic value? (. elegance,…) ? fit for purpose? (. fortable,…) ? All quality measures are relative – there is no absolute scale – we can say A is better than B but it is usually hard to say how much better ? For software: – construction quality(建造的品質(zhì) )? ? software is not manufactured – aesthetic value (美學(xué)上的價(jià)值 )? ? but most of the software is invisible ? aesthetic value matters for the user interface, but is only a marginal concern – fit for purpose? ? Need to understand the purpose 軟體品質(zhì)因素 Measuring Quality The Quality Concepts (abstract notions of quality properties) Measurable Quantities (define some metrics) Counts taken from Design Representations (realization of the metrics) usability minutes taken for some user task??? time taken to learn how to use? plexity count procedure calls??? information flow between modules? reliability run it and count crashes per hour??? mean time to failure? examples... Four Key Quality Concepts ? Reliability – designer must be able to predict how the system will behave: ? pleteness does it do everything it is supposed to do? (. handle all possible inputs) ? consistency does it always behave as expected? (. repeatability) ? robustness does it behave well under abnormal conditions? (. resource failure) ? Efficiency – Use of resources such as processor time, memory, work bandwidth ? This is less important than reliability in most cases ? Maintainability – How easy will it be to modify in the future? ? perfective, adaptive, corrective ? Usability – How easy is it to use? McCall’ s Quality Factors operation Correctness reliability usability integrity efficiency Maintainability Flexibility Testability Portability Reusability Interoperability General utility portability Asis utility Maintainability reliability efficiency usability testability understandability modifiability deviceindependence selfcontainedness accuracy pleteness robustness/integrity consistency accountability device efficiency accessibility municativeness selfdescriptiveness structuredness conciseness legibility augmentability Source: See Blum, 1992, p176 Product operation usability Product revision Product transition integrity maintainability testability reusability portability interoperability operability training I/O volume Access control Access audit Storage efficiency consistency instrumentation expandability generality Selfdescriptiveness modularity machine independence s/w system independence ms. monality efficiency correctness reliability flexibility municatativeness I/O rate execution efficiency Source: See van Vliet 2023, pp1113 traceability pleteness accuracy error tolerance simplicity conciseness data monality Measurable Predictors of Quality ? Simplicity – the design meets its objectives and has no extra embellishments – can be measured by looking for its converse, plexity: ? control flow plexity (number of paths through the program) ? information flow plexity (number of data items shared) ? name space plexity (number of different identifiers and operators) ? Modularity – different concerns within the design have been separated – can be measured by looking at: ? cohesion (how well ponents of a module go together) ? coupling (how much different modules have to municate) Quality and how to achieve it ? Product quality – always an issue ? ? After WWII, industry in the US and elsewhere has substantially improved quality via extensive testing and statistical quality control ? Japanese industry has followed a different concept, . total quality initiative (Deming, Juran), where quality control is an intrinsic aspect of the production process, not a postproduction activity ? In other words