Kĩ thuật lập trình - Chapter 24: Quality management

Chapter 24 - Quality ManagementLecture 11Chapter 24 Quality managementTopics coveredSoftware qualitySoftware standardsReviews and inspectionsSoftware measurement and metrics2Chapter 24 Quality managementSoftware quality managementConcerned with ensuring that the required level of quality is achieved in a software product.Three principal concerns:At the organizational level, quality management is concerned with establishing a framework of organizational processes and standards that will lead to high-quality software. At the project level, quality management involves the application of specific quality processes and checking that these planned processes have been followed. At the project level, quality management is also concerned with establishing a quality plan for a project. The quality plan should set out the quality goals for the project and define what processes and standards are to be used. 3Chapter 24 Quality managementQuality management activitiesQuality management provides an independent check on the software development process. The quality management process checks the project deliverables to ensure that they are consistent with organizational standards and goals The quality team should be independent from the development team so that they can take an objective view of the software. This allows them to report on software quality without being influenced by software development issues. 4Chapter 24 Quality managementQuality management and software development 5Chapter 24 Quality managementQuality planningA quality plan sets out the desired product qualities and how these are assessed and defines the most significant quality attributes.The quality plan should define the quality assessment process.It should set out which organisational standards should be applied and, where necessary, define new standards to be used.6Chapter 24 Quality managementQuality plansQuality plan structureProduct introduction;Product plans;Process descriptions;Quality goals;Risks and risk management.Quality plans should be short, succinct documentsIf they are too long, no-one will read them.7Chapter 24 Quality managementScope of quality managementQuality management is particularly important for large, complex systems. The quality documentation is a record of progress and supports continuity of development as the development team changes.For smaller systems, quality management needs less documentation and should focus on establishing a quality culture.8Chapter 24 Quality managementSoftware qualityQuality, simplistically, means that a product should meet its specification.This is problematical for software systemsThere is a 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.The focus may be ‘fitness for purpose’ rather than specification conformance.9Chapter 24 Quality managementSoftware fitness for purposeHave programming and documentation standards been followed in the development process?Has the software been properly tested?Is the software sufficiently dependable to be put into use?Is the performance of the software acceptable for normal use? Is the software usable?Is the software well-structured and understandable?10Chapter 24 Quality managementSoftware quality attributesSafetyUnderstandabilityPortabilitySecurityTestabilityUsabilityReliabilityAdaptabilityReusabilityResilienceModularityEfficiencyRobustnessComplexityLearnability11Chapter 24 Quality managementQuality conflictsIt is not possible for any system to be optimized for all of these attributes – for example, improving robustness may lead to loss of performance. The quality plan should therefore define the most important quality attributes for the software that is being developed. The plan should also include a definition of the quality assessment process, an agreed way of assessing whether some quality, such as maintainability or robustness, is present in the product. 12Chapter 24 Quality managementProcess and product qualityThe quality of a developed product is influenced by the quality of the production process.This is important in software development as some product quality attributes are hard to assess.However, there is a very complex and poorly understood relationship between software processes and product quality.The application of individual skills and experience is particularly important in software development;External factors such as the novelty of an application or the need for an accelerated development schedule may impair product quality.13Chapter 24 Quality managementProcess-based quality 14Chapter 24 Quality managementSoftware standardsStandards define the required attributes of a product or process. They play an important role in quality management.Standards may be international, national, organizational or project standards.Product standards define characteristics that all software components should exhibit e.g. a common programming style.Process standards define how the software process should be enacted.15Chapter 24 Quality managementImportance of standardsEncapsulation of best practice- avoids repetition of past mistakes.They are a framework for defining what quality means in a particular setting i.e. that organization’s view of quality.They provide continuity - new staff can understand the organisation by understanding the standards that are used.16Chapter 24 Quality managementProduct and process standards Product standardsProcess standardsDesign review formDesign review conductRequirements document structureSubmission of new code for system buildingMethod header formatVersion release processJava programming styleProject plan approval processProject plan formatChange control processChange request formTest recording process17Chapter 24 Quality managementProblems with standardsThey may not be seen as relevant and up-to-date by software engineers.They often involve too much bureaucratic form filling.If they are unsupported by software tools, tedious form filling work is often involved to maintain the documentation associated with the standards.18Chapter 24 Quality managementStandards developmentInvolve 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 specialized tool support. Excessive clerical work is the most significant complaint against standards. Web-based forms are not good enough.19Chapter 24 Quality managementISO 9001 standards frameworkAn international set of standards that can be used as a basis for developing quality management systems.ISO 9001, the most general of these standards, applies to organizations that design, develop and maintain products, including software. The ISO 9001 standard is a framework for developing software standards. It sets out general quality principles, describes quality processes in general and lays out the organizational standards and procedures that should be defined. These should be documented in an organizational quality manual.20Chapter 24 Quality managementISO 9001 core processes 21Chapter 24 Quality managementISO 9001 and quality management 22Chapter 24 Quality managementISO 9001 certificationQuality standards and procedures should be documented in an organisational quality manual.An external body may certify that an organisation’s quality manual conforms to ISO 9000 standards.Some customers require suppliers to be ISO 9000 certified although the need for flexibility here is increasingly recognised.23Chapter 24 Quality managementKey pointsSoftware quality management is concerned with ensuring that software has a low number of defects and that it reaches the required standards of maintainability, reliability, portability and so on. SQM includes defining standards for processes and products and establishing processes to check that these standards have been followed. Software standards are important for quality assurance as they represent an identification of ‘best practice’. Quality management procedures may be documented in an organizational quality manual, based on the generic model for a quality manual suggested in the ISO 9001 standard.24Chapter 24 Quality managementChapter 24 - Quality ManagementLecture 225Chapter 24 Quality managementReviews and inspectionsA group examines part or all of a process or system and its documentation to find potential problems.Software or documents may be 'signed off' at a review which signifies that progress to the next development stage has been approved by management.There are different types of review with different objectivesInspections for defect removal (product);Reviews for progress assessment (product and process);Quality reviews (product and standards).26Chapter 24 Quality managementQuality reviewsA group of people carefully examine part or all of a software system and its associated documentation.Code, designs, specifications, test plans, standards, etc. can all be reviewed.Software or documents may be 'signed off' at a review which signifies that progress to the next development stage has been approved by management.27Chapter 24 Quality managementThe software review process 28Chapter 24 Quality managementReviews and agile methodsThe review process in agile software development is usually informal. In Scrum, for example, there is a review meeting after each iteration of the software has been completed (a sprint review), where quality issues and problems may be discussed. In extreme programming, pair programming ensures that code is constantly being examined and reviewed by another team member. XP relies on individuals taking the initiative to improve and refactor code. Agile approaches are not usually standards-driven, so issues of standards compliance are not usually considered.29Chapter 24 Quality managementProgram inspectionsThese are peer reviews where engineers examine the source of a system with the aim of discovering anomalies and defects.Inspections do not require execution of a system so may be used before implementation.They may be applied to any representation of the system (requirements, design,configuration data, test data, etc.).They have been shown to be an effective technique for discovering program errors.30Chapter 24 Quality managementInspection checklistsChecklist of common errors should be used to drive the inspection.Error checklists are programming language dependent and reflect the characteristic errors that are likely to arise in the language.In general, the 'weaker' the type checking, the larger the checklist.Examples: Initialisation, Constant naming, loop termination, array bounds, etc.31Chapter 24 Quality managementAn inspection checklist (a)Fault classInspection checkData faultsAre all program variables initialized before their values are used?Have all constants been named?Should the upper bound of arrays be equal to the size of the array or Size -1?If character strings are used, is a delimiter explicitly assigned?Is there any possibility of buffer overflow? Control faultsFor each conditional statement, is the condition correct?Is each loop certain to terminate?Are compound statements correctly bracketed?In case statements, are all possible cases accounted for?If a break is required after each case in case statements, has it been included?Input/output faultsAre all input variables used?Are all output variables assigned a value before they are output?Can unexpected inputs cause corruption?32Chapter 24 Quality managementAn inspection checklist (b)Fault classInspection checkInterface faultsDo all function and method calls have the correct number of parameters?Do formal and actual parameter types match? Are the parameters in the right order? If components access shared memory, do they have the same model of the shared memory structure?Storage management faultsIf a linked structure is modified, have all links been correctly reassigned?If dynamic storage is used, has space been allocated correctly?Is space explicitly deallocated after it is no longer required?Exception management faultsHave all possible error conditions been taken into account?33Chapter 24 Quality managementAgile methods and inspectionsAgile processes rarely use formal inspection or peer review processes. Rather, they rely on team members cooperating to check each other’s code, and informal guidelines, such as ‘check before check-in’, which suggest that programmers should check their own code. Extreme programming practitioners argue that pair programming is an effective substitute for inspection as this is, in effect, a continual inspection process. Two people look at every line of code and check it before it is accepted.34Chapter 24 Quality managementSoftware measurement and metricsSoftware measurement is concerned with deriving a numeric value for an attribute of a software product or process.This allows for objective comparisons between techniques and processes.Although some companies have introduced measurement programmes, most organisations still don’t make systematic use of software measurement.There are few established standards in this area.35Chapter 24 Quality managementSoftware metricAny type of measurement which relates to a software system, process or related documentationLines of code in a program, the Fog index, number of person-days required to develop a component.Allow the software and the software process to be quantified.May be used to predict product attributes or to control the software process.Product metrics can be used for general predictions or to identify anomalous components.36Chapter 24 Quality managementPredictor and control measurements 37Chapter 24 Quality managementUse of measurementsTo assign a value to system quality attributes By measuring the characteristics of system components, such as their cyclomatic complexity, and then aggregating these measurements, you can assess system quality attributes, such as maintainability.To identify the system components whose quality is sub-standard Measurements can identify individual components with characteristics that deviate from the norm. For example, you can measure components to discover those with the highest complexity. These are most likely to contain bugs because the complexity makes them harder to understand. 38Chapter 24 Quality managementMetrics assumptionsA software property can be measured.The relationship exists between what we can measure and what we want to know. We can only measure internal attributes but are often more interested in external software attributes.This relationship has been formalised and validated.It may be difficult to relate what can be measured to desirable external quality attributes.39Chapter 24 Quality managementRelationships between internal and external software 40Chapter 24 Quality managementProblems with measurement in industryIt is impossible to quantify the return on investment of introducing an organizational metrics program. There are no standards for software metrics or standardized processes for measurement and analysis. In many companies, software processes are not standardized and are poorly defined and controlled. Most work on software measurement has focused on code-based metrics and plan-driven development processes. However, more and more software is now developed by configuring ERP systems or COTS.Introducing measurement adds additional overhead to processes. 41Chapter 24 Quality managementProduct metricsA quality metric should be a predictor of product quality.Classes of product metricDynamic metrics which are collected by measurements made of a program in execution;Static metrics which are collected by measurements made of the system representations;Dynamic metrics help assess efficiency and reliabilityStatic metrics help assess complexity, understandability and maintainability.42Chapter 24 Quality managementDynamic and static metricsDynamic metrics are closely related to software quality attributesIt is relatively easy to measure the response time of a system (performance attribute) or the number of failures (reliability attribute).Static metrics have an indirect relationship with quality attributesYou need to try and derive a relationship between these metrics and properties such as complexity, understandability and maintainability.43Chapter 24 Quality managementStatic software product metricsSoftware metricDescriptionFan-in/Fan-outFan-in is a measure of the number of functions or methods that call another function or method (say X). Fan-out is the number of functions that are called by function X. A high value for fan-in means that X is tightly coupled to the rest of the design and changes to X will have extensive knock-on effects. A high value for fan-out suggests that the overall complexity of X may be high because of the complexity of the control logic needed to coordinate the called components.Length of codeThis is a measure of the size of a program. Generally, the larger the size of the code of a component, the more complex and error-prone that component is likely to be. Length of code has been shown to be one of the most reliable metrics for predicting error-proneness in components.44Chapter 24 Quality managementStatic software product metricsSoftware metricDescriptionCyclomatic complexityThis is a measure of the control complexity of a program. This control complexity may be related to program understandability. I discuss cyclomatic complexity in Chapter 8.Length of identifiersThis is a measure of the average length of identifiers (names for variables, classes, methods, etc.) in a program. The longer the identifiers, the more likely they are to be meaningful and hence the more understandable the program.Depth of conditional nestingThis is a measure of the depth of nesting of if-statements in a program. Deeply nested if-statements are hard to understand and potentially error-prone.Fog indexThis is a measure of the average length of words and sentences in documents. The higher the value of a document’s Fog index, the more difficult the document is to understand.45Chapter 24 Quality managementThe CK object-oriented metrics suite Object-oriented metricDescriptionWeighted methods per class (WMC)This is the number of methods in each class, weighted by the complexity of each method. Therefore, a simple method may have a complexity of 1, and a large and complex method a much higher value. The larger the value for this metric, the more complex the object class. Complex objects are more likely to be difficult to understand. They may not be logically cohesive, so cannot be reused effectively as superclasses in an inheritance tree.Depth of inheritance tree (DIT)This represents the number of discrete levels in the inheritance tree where subclasses inherit attributes and operations (methods) from superclasses. The deeper the inheritance tree, the more complex the design. Many object classes may have to be understood to understand the object classes at the leaves of the tree. Number of children (NOC)This is a measure of the number of immediate subclasses in a class. It measures the breadth of a class hierarchy, whereas DIT measures its depth. A high value for NOC may indicate greater reuse. It may mean that more effort should be made in validating base classes because of the number of subclasses that depend on them.46Chapter 24 Quality managementThe CK object-oriented metrics suite Object-oriented metricDescriptionCoupling between object classes (CBO)Classes are coupled when methods in one class use methods or instance variables defined in a different class. CBO is a measure of how much coupling exists. A high value for CBO means that classes are highly dependent, and therefore it is more likely that changing one class will affect other classes in the program.Response for a class (RFC)RFC is a measure of the number of methods that could potentially be executed in response to a message received by an object of that class. Again, RFC is related to complexity. The higher the value for RFC, the more complex a class and hence the more likely it is that it will include errors.Lack of cohesion in methods (LCOM)LCOM is calculated by considering pairs of methods in a class. LCOM is the difference between the number of method pairs without shared attributes and the number of method pairs with shared attributes. The value of this metric has been widely debated and it exists in several variations. It is not clear if it really adds any additional, useful information over and above that provided by other metrics.47Chapter 24 Quality managementSoftware component analysisSystem component can be analyzed separately using a range of metrics. The values of these metrics may then compared for different components and, perhaps, with historical measurement data collected on previous projects.Anomalous measurements, which deviate significantly from the norm, may imply that there are problems with the quality of these components. 48Chapter 24 Quality managementThe process of product measurement 49Chapter 24 Quality managementMeasurement surprisesReducing the number of faults in a program leads to an increased number of help desk callsThe program is now thought of as more reliable and so has a wider more diverse market. The percentage of users who call the help desk may have decreased but the total may increase;A more reliable system is used in a different way from a system where users work around the faults. This leads to more help desk calls.50Chapter 24 Quality managementKey pointsReviews of the software process deliverables involve a team of people who check that quality standards are being followed. In a program inspection or peer review, a small team systematically checks the code. They read the code in detail and look for possible errors and omissionsSoftware measurement can be used to gather data about software and software processes. Product quality metrics are particularly useful for highlighting anomalous components that may have quality problems. 51Chapter 24 Quality management