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CSC-3325: Chapter 6. Title : The Software Quality Reading: I. Sommerville , Chap: 24. Topics covered. Software Quality management Process of quality assurance Quality reviews Software standards Software metrics Product quality metrics. Software quality management.
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CSC-3325: Chapter 6 Title : The Software Quality Reading: I. Sommerville, Chap: 24 Dr Driss Kettani, from I. Sommerville
Topics covered • Software Quality management • Process of quality assurance • Quality reviews • Software standards • Software metrics • Product quality metrics Dr Driss Kettani, from I. Sommerville
Software quality management • Concerned with ensuring that the required level of quality is achieved in a software product • Involves defining appropriate quality standards and procedures and ensuring that these are followed • Should aim to develop a ‘quality culture’ where quality is seen as everyone’s responsibility Dr Driss Kettani, from I. Sommerville
What is quality? • In its simple understanding, Quality means that a product should meet its specification • This is problematical for software systems • Tension between customer quality requirements (efficiency, reliability, etc.) and developer quality requirements (maintainability, reusability, etc.) • Some quality requirements are difficult to specify in an unambiguous way • Software specifications are usually incomplete and often inconsistent Dr Driss Kettani, from I. Sommerville
Software quality attributes Dr Driss Kettani, from I. Sommerville
Quality management activities • Quality assurance • Establish organizational procedures and standards for quality • Quality planning • Select applicable procedures and standards for a particular project and modify these as required • Quality control • Ensure that procedures and standards are followed by the software development team Dr Driss Kettani, from I. Sommerville
ISO 9000 • ISO 9000 is an iinternational set ofstandards for quality management in all industries … • Applicable to a range of organizations from manufacturing to service industries… • Each country has its own version… • ISO 9001 applicable to organizations which design, develop and maintain products… • It is a generic model of the quality process… Must be instantiated for each organization… • ISO 9000-3 interprets ISO 9000 for software engineering… Dr Driss Kettani, from I. Sommerville
ISO 9000 certification • Quality standards and procedures should be documented in an organizational quality manual • External body may certify that anorganisation’s quality manual conforms to ISO 9000 standards • Customers are, increasingly, demanding that suppliers are ISO 9000 certified Dr Driss Kettani, from I. Sommerville
ISO 9000 and quality management Dr Driss Kettani, from I. Sommerville
Process quality assurance • The quality of a developed product is influenced by the quality of the production process • Particularly important in software development as some product quality attributes are hard to assess • However, there is a very complex and poorly understood relation between software processes and product quality… Dr Driss Kettani, from I. Sommerville
Quality reviews • The principal method of validating the quality of a process or of a product • Group examined part or all of a process or system and its documentation to find potential problems • There are different types of review with different objectives • Inspections for defect removal (product) • Reviews for progress assessment(product and process) • Quality reviews (product and standards) Dr Driss Kettani, from I. Sommerville
Quality reviews • Objective is the discovery of system defects and inconsistencies • Any documents produced in the process may be reviewed • Review teams should be relatively small and reviews should be fairly short • Review should be recorded and records maintained Dr Driss Kettani, from I. Sommerville
Review results • Comments made during the review should be documented and classified: • No action. No change to the software or documentation is required. • Refer for repair. Designer or programmer should correct an identified fault. • Reconsider overall design. The problem identified in the review impacts other parts of the design. Some overall judgement must be made about the most cost-effective way of solving the problem. Dr Driss Kettani, from I. Sommerville
Software standards • Key to effective quality management • May be international, national, organizational or project • Product standards define characteristics that all components should exhibit e.g. a common programming style • Process standards define how the software process should be conducted Dr Driss Kettani, from I. Sommerville
Importance of standards • Encapsulation of best practice. Avoids repetition of past mistakes • Framework for QA process - it involves checking standard compliance • Provide continuity. New staff can understand the organisation by understand the standards applied Dr Driss Kettani, from I. Sommerville
Problems with standards • Not seen as relevant and up-to-date by software engineers • Involve too much bureaucratic form filling • Unsupported by software tools and manual work is involved to maintain standards Dr Driss Kettani, from I. Sommerville
Standards development • Involve practitioners in development • Engineers should understand the rationale underlying a standard • Review standards and their usage regularly. Standards can quickly become outdated and this reduces their credibility amongst practitioners • Detailed standards should have associated tool support. Excessive clerical work is the most significant complaint against standards Dr Driss Kettani, from I. Sommerville
Software metrics • Any type of measurement which relates to a software system, process or related documentation • Lines of code in a program, number of person-days required to develop a component, the number of errors per module… • Allow the software and the software process to be quantified • Measures of the software process or product • Should be captured automatically if possible Dr Driss Kettani, from I. Sommerville
Metrics assumptions • A software property can be measured • It isdifficult to relate what can be measured todesirable quality attributes • There is a relationship between what we can measure and what we want to know • This relationship has been formalized and validated Dr Driss Kettani, from I. Sommerville
Internal and external attributes Dr Driss Kettani, from I. Sommerville
Design Metrics • Cohesion • How closely are the parts of a component related • Coupling • How independent is a component • Understandability • How easy is it to understand a component’s function • Adaptability • How easy is to change a component Dr Driss Kettani, from I. Sommerville
Validation of quality metrics The whole area is still a research area rather than practically applicable. Dr Driss Kettani, from I. Sommerville
Programs quality metrics • Design metrics also applicable to programs • Other metrics include • Length. The size of the program source code • Cyclomatic complexity. The complexity of program control • Length of identifiers • Depth of conditional nesting • Anomalous metric values suggest a component may contain an above average number of defects or may be difficult to understand Dr Driss Kettani, from I. Sommerville
Common Metrics for programs • Length of code is simple but experiments have suggested it is a good predictor of problems • Cyclomatic complexity can be misleading • Long names should increase program understandability • Deeply nested conditionals are hard to understand. May be a contributor to an understandability index Dr Driss Kettani, from I. Sommerville
Problems with Metrics • Metrics still have a limited value and are not widely collected • Relationships between what we can measure and what we want to know are not well-understood • Lack of commonality across software process between organizations makes universal metrics difficult to develop Dr Driss Kettani, from I. Sommerville
Key points • Software quality management is concerned with ensuring that software meets its required standards • Quality assurance procedures should be documented in an organisational quality manual • A project quality plan should identify project-specific quality requirements • Software standards are an encapsulation of best practice Dr Driss Kettani, from I. Sommerville
Key points • Reviews are the principal means of implementing quality assurance • Metrics gather information about both process and product • Control metrics provide management information about the software project. Predictor metrics allow product attributes to be estimated • Quality metrics should be used to identify potentially problematical components Dr Driss Kettani, from I. Sommerville