1、Part 1Quality Management1Topics coveredSoftware qualitySoftware standardsReviews and inspectionsSoftware measurement and metrics2Software quality managementConcerned with ensuring that the required level of quality is achieved in a software product.Three principal concerns:At the organizational leve

2、l, 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 follo

3、wed.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.3Quality management activitiesQuality management provides an indepen

4、dent 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 so

5、ftware. This allows them to report on software quality without being influenced by software development issues.4Quality management and software development5Quality plansQuality plan structureProduct introduction;Product plans;Process descriptions;Quality goals;Risks and risk management.Quality plans

6、 should be short, succinct documentsIf they are too long, no-one will read them.7Scope 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 change

7、s.For smaller systems, quality management needs less documentation and should focus on establishing a quality culture.8Software fitness for purposeHave programming and documentation standards been followed in the development process?Has the software been properly tested?Is the software sufficiently

8、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?10Software quality attributesSafetyUnderstandabilityPortabilitySecurityTestabilityUsabilityReliabilityAdaptabilityReusabilityResilienc

9、eModularityEfficiencyRobustnessComplexityLearnability11Quality 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 t

10、he 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.12Process-based quality14Software standardsStandards define the required

11、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 d

12、efine how the software process should be enacted.15Product and process standardsProduct standardsProcess standardsDesign review formDesign review conductRequirements document structureSubmission of new code for system buildingMethod header formatVersion release processJava programming styleProject p

13、lan approval processProject plan formatChange control processChange request formTest recording process17Problems 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, tediou

14、s form filling work is often involved to maintain the documentation associated with the standards.18Standards developmentInvolve practitioners in development. Engineers should understand the rationale underlying a standard.Review standards and their usage regularly. Standards can quickly become outd

15、ated 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.19ISO 9001 standards frameworkAn international set of standards that

16、 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

17、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.20ISO 9001 core processes21ISO 9001 and quality management22Key pointsSoftware quality management is conc

18、erned 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. Soft

19、ware 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.24Part 2Quality Management25

20、Quality 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 developmen

21、t stage has been approved by management.27The software review processPre-Review Activities28Reviews 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

22、 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 stand

23、ards-driven, so issues of standards compliance are not usually considered.29Program 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

24、.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.30Inspection checklistsChecklist of common errors should be used to drive the inspection.Error checkli

25、sts 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.31An Inspection Checklist (a)Fault c

26、lassInspection 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

27、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 includ

28、ed?Input/output faultsAre all input variables used?Are all output variables assigned a value before they are output?Can unexpected inputs cause corruption?32An Inspection Checklist (b)Fault classInspection checkInterface faultsDo all function and method calls have the correct number of parameters?Do

29、 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 u

30、sed, 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?33Agile methods and inspectionsAgile processes rarely use formal inspection or peer review processes.Rather, th

31、ey rely on team members cooperating to check each others 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 eff

32、ect, a continual inspection process.Two people look at every line of code and check it before it is accepted.34Software 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 betwe

33、en techniques and processes.Although some companies have introduced measurement programmes, most organisations still dont make systematic use of software measurement.There are few established standards in this area.35Software metricAny type of measurement which relates to a software system, process

34、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 p

35、redictions or to identify anomalous components.36Predictor and control measurements37Use of measurementsTo assign a value to system quality attributesBy measuring the characteristics of system components, such as their cyclomatic complexity(循環(huán)復(fù)雜度), and then aggregating these measurements, you can as

36、sess system quality attributes, such as maintainability.To identify the system components whose quality is sub-standardMeasurements can identify individual components with characteristics that deviate from the norm. For example, you can measure components to discover those with the highest complexit

37、y. These are most likely to contain bugs because the complexity makes them harder to understand. 38Metrics 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 intereste

38、d 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.39Relationships between internal and external software40Problems with measurement in industryIt is impossible to quantify

39、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 measurem

40、ent 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. 41Product metricsA quality metric should be a predictor of product quality.C

41、lasses 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, understandabil

42、ity and maintainability.42Dynamic 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

43、with quality attributesYou need to try and derive a relationship between these metrics and properties such as complexity, understandability and maintainability.43Static software product metricsSoftware metricDescriptionFan-in/Fan-outFan-in is a measure of the number of functions or methods that call

44、 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 complexit

45、y 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

46、 code has been shown to be one of the most reliable metrics for predicting error-proneness in components.44Static software product metricsSoftware metricDescriptionCyclomatic complexityThis is a measure of the control complexity of a program. This control complexity may be related to program underst

47、andability. 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

48、 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

49、 documents Fog index, the more difficult the document is to understand.45The CK object-oriented metrics suiteObject-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

50、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 inher

51、itance 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