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Quality Management




©Ian Sommerville 2004       Software Engineering, 7th edition. Chapter 27   Slide 1
Objectives
     q     To introduce the quality management process and
           key quality management activities
     q     To explain the role of standards in quality
           management
     q     To explain the concept of a software metric,
           predictor metrics and control metrics
     q     To explain how measurement may be used in
           assessing software quality and the limitations of
           software measurement




©Ian Sommerville 2004    Software Engineering, 7th edition. Chapter 27   Slide 2
Topics covered
    q     Process and product quality
    q     Quality assurance and standards
    q     Quality planning
    q     Quality control




©Ian Sommerville 2004     Software Engineering, 7th edition. Chapter 27   Slide 3
Software quality management
     q     Concerned with ensuring that the required
           level of quality is achieved in a software
           product.
     q     Involves defining appropriate quality
           standards and procedures and ensuring that
           these are followed.
     q     Should aim to develop a ‘quality culture’
           where quality is seen as everyone’s
           responsibility.


©Ian Sommerville 2004   Software Engineering, 7th edition. Chapter 27   Slide 4
What is quality?

  q     Quality, simplistically, means that a product should
        meet its specification.
  q     This is problematical for software systems
          •     There 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.




©Ian Sommerville 2004         Software Engineering, 7th edition. Chapter 27   Slide 5
The quality compromise
     q     We cannot wait for specifications to improve
           before paying attention to quality
           management.
     q     We must put quality management
           procedures into place to improve quality in
           spite of imperfect specification.




©Ian Sommerville 2004   Software Engineering, 7th edition. Chapter 27   Slide 6
Scope of quality management
     q     Quality 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.
     q     For smaller systems, quality management
           needs less documentation and should focus
           on establishing a quality culture.



©Ian Sommerville 2004   Software Engineering, 7th edition. Chapter 27   Slide 7
Quality management activities
     q     Quality assurance
             •     Establish organisational procedures and standards for
                   quality.
     q     Quality planning
             •     Select applicable procedures and standards for a
                   particular project and modify these as required.
     q     Quality control
             •     Ensure that procedures and standards are followed by
                   the software development team.
     q     Quality management should be separate from
           project management to ensure independence.



©Ian Sommerville 2004         Software Engineering, 7th edition. Chapter 27   Slide 8
Quality management and software development




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©Ian Sommerville 2004   Software Engineering, 7th edition. Chapter 27   Slide 9
Process and product quality
     q     The quality of a developed product is
           influenced by the quality of the production
           process.
     q     This is important in software development as
           some product quality attributes are hard to
           assess.
     q     However, there is a very complex and poorly
           understood relationship between software
           processes and product quality.


©Ian Sommerville 2004   Software Engineering, 7th edition. Chapter 27   Slide 10
Process-based quality
     q     There is a straightforward link between process and
           product in manufactured goods.
     q     More complex for software because:
             •     The application of individual skills and experience is
                   particularly imporant in software development;
             •     External factors such as the novelty of an application or
                   the need for an accelerated development schedule may
                   impair product quality.
     q     Care must be taken not to impose inappropriate
           process standards - these could reduce rather than
           improve the product quality.


©Ian Sommerville 2004          Software Engineering, 7th edition. Chapter 27   Slide 11
Process-based quality


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©Ian Sommerville 2004   Software Engineering, 7th edition. Chapter 27   Slide 12
Practical process quality
     q     Define process standards such as how
           reviews should be conducted, configuration
           management, etc.
     q     Monitor the development process to ensure
           that standards are being followed.
     q     Report on the process to project
           management and software procurer.
     q     Don’t use inappropriate practices simply
           because standards have been established.


©Ian Sommerville 2004   Software Engineering, 7th edition. Chapter 27   Slide 13
Quality assurance and standards
     q     Standards are the key to effective quality
           management.
     q     They may be international, national,
           organizational or project standards.
     q     Product standards define characteristics that
           all components should exhibit e.g. a common
           programming style.
     q     Process standards define how the software
           process should be enacted.


©Ian Sommerville 2004   Software Engineering, 7th edition. Chapter 27   Slide 14
Importance of standards
     q     Encapsulation of best practice- avoids
           repetition of past mistakes.
     q     They are a framework for quality assurance
           processes - they involve checking
           compliance to standards.
     q     They provide continuity - new staff can
           understand the organisation by
           understanding the standards that are used.



©Ian Sommerville 2004   Software Engineering, 7th edition. Chapter 27   Slide 15
Product and process standards




©Ian Sommerville 2004   Software Engineering, 7th edition. Chapter 27   Slide 16
Problems with standards
     q     They may not be seen as relevant and up-to-
           date by software engineers.
     q     They often involve too much bureaucratic
           form filling.
     q     If they are unsupported by software tools,
           tedious manual work is often involved to
           maintain the documentation associated with
           the standards.



©Ian Sommerville 2004   Software Engineering, 7th edition. Chapter 27   Slide 17
Standards development
     q     Involve practitioners in development. Engineers
           should understand the rationale underlying a
           standard.
     q     Review standards and their usage regularly.
           Standards can quickly become outdated and this
           reduces their credibility amongst practitioners.
     q     Detailed standards should have associated tool
           support. Excessive clerical work is the most
           significant complaint against standards.




©Ian Sommerville 2004    Software Engineering, 7th edition. Chapter 27   Slide 18
ISO 9000
     q     An international set of standards for quality
           management.
     q     Applicable to a range of organisations from
           manufacturing to service industries.
     q     ISO 9001 applicable to organisations which
           design, develop and maintain products.
     q     ISO 9001 is a generic model of the quality
           process that must be instantiated for each
           organisation using the standard.


©Ian Sommerville 2004   Software Engineering, 7th edition. Chapter 27   Slide 19
ISO 9001




©Ian Sommerville 2004   Software Engineering, 7th edition. Chapter 27   Slide 20
ISO 9000 certification
  q     Quality standards and procedures should be
        documented in an organisational quality
        manual.
  q     An external body may certify that an
        organisation’s quality manual conforms to
        ISO 9000 standards.
  q     Some customers require suppliers to be ISO
        9000 certified although the need for flexibility
        here is increasingly recognised.

©Ian Sommerville 2004    Software Engineering, 7th edition. Chapter 27   Slide 21
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©Ian Sommerville 2004   Software Engineering, 7th edition. Chapter 27   Slide 22
Documentation standards
     q     Particularly important - documents are the tangible
           manifestation of the software.
     q     Documentation process standards
             •     Concerned with how documents should be developed,
                   validated and maintained.
     q     Document standards
             •     Concerned with document contents, structure, and
                   appearance.
     q     Document interchange standards
             •     Concerned with the compatibility of electronic documents.




©Ian Sommerville 2004          Software Engineering, 7th edition. Chapter 27   Slide 23
Documentation process


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©Ian Sommerville 2004   Software Engineering, 7th edition. Chapter 27   Slide 24
Document standards
     q     Document identification standards
             •     How documents are uniquely identified.
     q     Document structure standards
             •     Standard structure for project documents.
     q     Document presentation standards
             •     Define fonts and styles, use of logos, etc.
     q     Document update standards
             •     Define how changes from previous versions are
                   reflected in a document.



©Ian Sommerville 2004        Software Engineering, 7th edition. Chapter 27   Slide 25
Document interchange standards
     q     Interchange standards allow electronic documents to
           be exchanged, mailed, etc.
     q     Documents are produced using different systems
           and on different computers. Even when standard
           tools are used, standards are needed to define
           conventions for their use e.g. use of style sheets and
           macros.
     q     Need for archiving. The lifetime of word processing
           systems may be much less than the lifetime of the
           software being documented. An archiving standard
           may be defined to ensure that the document can be
           accessed in future.


©Ian Sommerville 2004     Software Engineering, 7th edition. Chapter 27   Slide 26
Quality planning
     q     A quality plan sets out the desired product
           qualities and how these are assessed and
           defines the most significant quality attributes.
     q     The quality plan should define the quality
           assessment process.
     q     It should set out which organisational
           standards should be applied and, where
           necessary, define new standards to be used.



©Ian Sommerville 2004      Software Engineering, 7th edition. Chapter 27   Slide 27
Quality plans
     q     Quality plan structure
             •     Product introduction;
             •     Product plans;
             •     Process descriptions;
             •     Quality goals;
             •     Risks and risk management.
     q     Quality plans should be short, succinct
           documents
             •     If they are too long, no-one will read them.


©Ian Sommerville 2004        Software Engineering, 7th edition. Chapter 27   Slide 28
Software quality attributes




©Ian Sommerville 2004   Software Engineering, 7th edition. Chapter 27   Slide 29
Quality control
     q     This involves checking the software
           development process to ensure that
           procedures and standards are being
           followed.
     q     There are two approaches to quality control
             •     Quality reviews;
             •     Automated software assessment and software
                   measurement.




©Ian Sommerville 2004       Software Engineering, 7th edition. Chapter 27   Slide 30
Quality reviews
     q     This is the principal method of validating the quality
           of a process or of a product.
     q     A group examines part or all of a process or system
           and its documentation to find potential problems.
     q     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).




©Ian Sommerville 2004         Software Engineering, 7th edition. Chapter 27   Slide 31
Types of review


Review type             Principal purpose
Design or program       To detect detailed errors in the requirements, design or code. A checklist of
inspections             possible errors should drive the review.
Progress reviews        To provide information for management about the overall progress of the
                        project. This is b oth a process and a product review and is concerned with
                        costs, plans and schedules.
Quality reviews         To carry out a t echnical analysis of product components or documentation to
                        find mismatches between the specification and the component design, code or
                        documentation and to ensure that defined quality standards have been followed.




©Ian Sommerville 2004                  Software Engineering, 7th edition. Chapter 27           Slide 32
Quality reviews
     q     A group of people carefully examine part or all
           of a software system and its associated
           documentation.
     q     Code, designs, specifications, test plans,
           standards, etc. can all be reviewed.
     q     Software or documents may be 'signed off' at a
           review which signifies that progress to the next
           development stage has been approved by
           management.




©Ian Sommerville 2004      Software Engineering, 7th edition. Chapter 27   Slide 33
Review functions
     q     Quality function - they are part of the general
           quality management process.
     q     Project management function - they provide
           information for project managers.
     q     Training and communication function -
           product knowledge is passed between
           development team members.




©Ian Sommerville 2004      Software Engineering, 7th edition. Chapter 27   Slide 34
Quality reviews
     q     The objective is the discovery of system
           defects and inconsistencies.
     q     Any documents produced in the process may
           be reviewed.
     q     Review teams should be relatively small and
           reviews should be fairly short.
     q     Records should always be maintained of
           quality reviews.


©Ian Sommerville 2004      Software Engineering, 7th edition. Chapter 27   Slide 35
Review results
     q     Comments made during the review should be
           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;
     q     Requirements and specification errors may
           have to be referred to the client.


©Ian Sommerville 2004          Software Engineering, 7th edition. Chapter 27   Slide 36
Software measurement and metrics
     q     Software measurement is concerned with deriving a
           numeric value for an attribute of a software product
           or process.
     q     This allows for objective comparisons between
           techniques and processes.
     q     Although some companies have introduced
           measurement programmes, most organisations still
           don’t make systematic use of software
           measurement.
     q     There are few established standards in this area.


©Ian Sommerville 2004    Software Engineering, 7th edition. Chapter 27   Slide 37
Software metric

     q     Any type of measurement which relates to a
           software system, process or related documentation
             •     Lines of code in a program, the Fog index, number of
                   person-days required to develop a component.
     q     Allow the software and the software process to
           be quantified.
     q     May be used to predict product attributes or to
           control the software process.
     q     Product metrics can be used for general predictions
           or to identify anomalous components.


©Ian Sommerville 2004         Software Engineering, 7th edition. Chapter 27   Slide 38
Predictor and control metrics


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©Ian Sommerville 2004
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                        Software Engineering, 7th edition. Chapter 27   Slide 39
Metrics assumptions
     q     A software property can be measured.
     q     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.
     q     This relationship has been formalised and
           validated.
     q     It may be difficult to relate what can be measured to
           desirable external quality attributes.




©Ian Sommerville 2004     Software Engineering, 7th edition. Chapter 27   Slide 40
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©Ian Sommerville 2004   Software Engineering, 7th edition. Chapter 27   Slide 41
The measurement process
     q     A software measurement process may be
           part of a quality control process.
     q     Data collected during this process should be
           maintained as an organisational resource.
     q     Once a measurement database has been
           established, comparisons across projects
           become possible.




©Ian Sommerville 2004   Software Engineering, 7th edition. Chapter 27   Slide 42
Product measurement process


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©Ian Sommerville 2004   Software Engineering, 7th edition. Chapter 27   Slide 43
Data collection
     q     A metrics programme should be based on a
           set of product and process data.
     q     Data should be collected immediately (not in
           retrospect) and, if possible, automatically.
     q     Three types of automatic data collection
             •     Static product analysis;
             •     Dynamic product analysis;
             •     Process data collation.



©Ian Sommerville 2004       Software Engineering, 7th edition. Chapter 27   Slide 44
Data accuracy
     q     Don’t collect unnecessary data
             •     The questions to be answered should be
                   decided in advance and the required data
                   identified.
     q     Tell people why the data is being collected.
             •     It should not be part of personnel evaluation.
     q     Don’t rely on memory
             •     Collect data when it is generated not after a
                   project has finished.


©Ian Sommerville 2004        Software Engineering, 7th edition. Chapter 27   Slide 45
Product metrics
     q     A quality metric should be a predictor of
           product quality.
     q     Classes of product metric
             •     Dynamic 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 reliability;
                   static metrics help assess complexity, understandability
                   and maintainability.




©Ian Sommerville 2004          Software Engineering, 7th edition. Chapter 27   Slide 46
Dynamic and static metrics
     q     Dynamic metrics are closely related to software
           quality attributes
             •     It is relatively easy to measure the response time of a
                   system (performance attribute) or the number of failures
                   (reliability attribute).
     q     Static metrics have an indirect relationship with
           quality attributes
             •     You need to try and derive a relationship between these
                   metrics and properties such as complexity,
                   understandability and maintainability.




©Ian Sommerville 2004          Software Engineering, 7th edition. Chapter 27   Slide 47
Software product metrics
     Software metric                                             Description
  Fan in/Fan-out          Fan-in is a measure of the number of functions or methods that call some other 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 i s 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 m ay be high because of the complexity of the control
                          logic needed to coordinate the called components.
  Length of code          This 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.
  Cyclomatic complexity   This is a m easure of the control complexity of a program. This control complexity may
                          be related to program understandability. I discuss how to compute cyclomatic
                          complexity in Chapter 22.
  Length of identifiers   This is a measure of the average length of distinct identifiers in a p rogram. The longer
                          the identifiers, the more likely they are to be m eaningful and hence the more
                          understandable the program.
  Depth of conditional    This is a measure of the depth of nesting of if-statements in a program. Deeply nested if
  nesting                 statements are hard to understand and are potentially error-prone.
  Fog index               This is a measure of the average length of words and sentences in documents. The higher
                          the value for the Fog index, the more difficult the document is to understand.




©Ian Sommerville 2004                        Software Engineering, 7th edition. Chapter 27                              Slide 48
Object-oriented metrics
     Object-oriented        Description
     metric
     Depth of inheritance   This represents the number of discrete levels in the inheritance tree where sub-
     tree                   classes inherit attributes and operations (methods) from super-classes. The
                            deeper the inheritance tree, the more complex the design. Many different object
                            classes may have to be understood to understand the object classes at the leaves
                            of the tree.
     Method fan-in/fan-     This is directly related to fan-in and fan-out as described above and means
     out                    essentially the same thing. However, it may be appropriate to make a
                            distinction between calls from other methods within the object and calls from
                            external methods.
     Weighted methods       This is the number of methods that are included in a class weighted by the
     per class              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 more difficult to understand. They may not be logically cohesive so
                            cannot be reused effectively as super-classes in an inheritance tree.
     Number of              This is the number of operations in a super-class that are over-ridden in a sub-
     overriding             class. A high value for this metric indicates that the super-class used may not be
     operations             an appropriate parent for the sub-class.



©Ian Sommerville 2004                     Software Engineering, 7th edition. Chapter 27                   Slide 49
Measurement analysis
     q     It is not always obvious what data means
             •     Analysing collected data is very difficult.
     q     Professional statisticians should be
           consulted if available.
     q     Data analysis must take local circumstances
           into account.




©Ian Sommerville 2004         Software Engineering, 7th edition. Chapter 27   Slide 50
Measurement surprises
     q     Reducing the number of faults in a program
           leads to an increased number of help desk
           calls
             •     The 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.


©Ian Sommerville 2004        Software Engineering, 7th edition. Chapter 27   Slide 51
Key points
     q     Software quality management is concerned
           with ensuring that software meets its
           required standards.
     q     Quality assurance procedures should be
           documented in an organisational quality
           manual.
     q     Software standards are an encapsulation of
           best practice.
     q     Reviews are the most widely used approach
           for assessing software quality.

©Ian Sommerville 2004   Software Engineering, 7th edition. Chapter 27   Slide 52
Key points
     q     Software measurement gathers information
           about both the software process and the
           software product.
     q     Product quality metrics should be used to
           identify potentially problematical
           components.
     q     There are no standardised and universally
           applicable software metrics.



©Ian Sommerville 2004   Software Engineering, 7th edition. Chapter 27   Slide 53

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Ch27 (1)

  • 1. Quality Management ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 1
  • 2. Objectives q To introduce the quality management process and key quality management activities q To explain the role of standards in quality management q To explain the concept of a software metric, predictor metrics and control metrics q To explain how measurement may be used in assessing software quality and the limitations of software measurement ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 2
  • 3. Topics covered q Process and product quality q Quality assurance and standards q Quality planning q Quality control ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 3
  • 4. Software quality management q Concerned with ensuring that the required level of quality is achieved in a software product. q Involves defining appropriate quality standards and procedures and ensuring that these are followed. q Should aim to develop a ‘quality culture’ where quality is seen as everyone’s responsibility. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 4
  • 5. What is quality? q Quality, simplistically, means that a product should meet its specification. q This is problematical for software systems • There 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. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 5
  • 6. The quality compromise q We cannot wait for specifications to improve before paying attention to quality management. q We must put quality management procedures into place to improve quality in spite of imperfect specification. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 6
  • 7. Scope of quality management q Quality 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. q For smaller systems, quality management needs less documentation and should focus on establishing a quality culture. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 7
  • 8. Quality management activities q Quality assurance • Establish organisational procedures and standards for quality. q Quality planning • Select applicable procedures and standards for a particular project and modify these as required. q Quality control • Ensure that procedures and standards are followed by the software development team. q Quality management should be separate from project management to ensure independence. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 8
  • 9. Quality management and software development Softwar D1 DD4 D23 process Quality D5 process Standar Qualit Quali ts procedu plan ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 9
  • 10. Process and product quality q The quality of a developed product is influenced by the quality of the production process. q This is important in software development as some product quality attributes are hard to assess. q However, there is a very complex and poorly understood relationship between software processes and product quality. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 10
  • 11. Process-based quality q There is a straightforward link between process and product in manufactured goods. q More complex for software because: • The application of individual skills and experience is particularly imporant in software development; • External factors such as the novelty of an application or the need for an accelerated development schedule may impair product quality. q Care must be taken not to impose inappropriate process standards - these could reduce rather than improve the product quality. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 11
  • 12. Process-based quality Dequa vNo elop Ass odu DefineSt ocess sp produ e Ydi epr Improc o Qua v OK pr ocess e ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 12
  • 13. Practical process quality q Define process standards such as how reviews should be conducted, configuration management, etc. q Monitor the development process to ensure that standards are being followed. q Report on the process to project management and software procurer. q Don’t use inappropriate practices simply because standards have been established. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 13
  • 14. Quality assurance and standards q Standards are the key to effective quality management. q They may be international, national, organizational or project standards. q Product standards define characteristics that all components should exhibit e.g. a common programming style. q Process standards define how the software process should be enacted. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 14
  • 15. Importance of standards q Encapsulation of best practice- avoids repetition of past mistakes. q They are a framework for quality assurance processes - they involve checking compliance to standards. q They provide continuity - new staff can understand the organisation by understanding the standards that are used. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 15
  • 16. Product and process standards ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 16
  • 17. Problems with standards q They may not be seen as relevant and up-to- date by software engineers. q They often involve too much bureaucratic form filling. q If they are unsupported by software tools, tedious manual work is often involved to maintain the documentation associated with the standards. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 17
  • 18. Standards development q Involve practitioners in development. Engineers should understand the rationale underlying a standard. q Review standards and their usage regularly. Standards can quickly become outdated and this reduces their credibility amongst practitioners. q Detailed standards should have associated tool support. Excessive clerical work is the most significant complaint against standards. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 18
  • 19. ISO 9000 q An international set of standards for quality management. q Applicable to a range of organisations from manufacturing to service industries. q ISO 9001 applicable to organisations which design, develop and maintain products. q ISO 9001 is a generic model of the quality process that must be instantiated for each organisation using the standard. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 19
  • 20. ISO 9001 ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 20
  • 21. ISO 9000 certification q Quality standards and procedures should be documented in an organisational quality manual. q An external body may certify that an organisation’s quality manual conforms to ISO 9000 standards. q Some customers require suppliers to be ISO 9000 certified although the need for flexibility here is increasingly recognised. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 21
  • 22. Ited a S docu O 900 qualit ISO 9000 and quality management instan Or qu ganis tion Or qualitga ti ualte isequaoc vPr 1 lop used ins PrSupp ojectge Pr Pr oject ojec oj quality qualit tsma ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 22
  • 23. Documentation standards q Particularly important - documents are the tangible manifestation of the software. q Documentation process standards • Concerned with how documents should be developed, validated and maintained. q Document standards • Concerned with document contents, structure, and appearance. q Document interchange standards • Concerned with the compatibility of electronic documents. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 23
  • 24. Documentation process Stage d aR1 Creatio CrwIncor Rie eaf te d eaAvie-d tevecomm epr doc dre aftpr aftw initialdo ofina vChec d 2 Stage Plishing o Autco Praft oofrdoc ead aft Pr oduce tevpr xt d final pwPr o ie Pr e print Stage teR 3 Pr oductio La oduc yut o la e v xty o ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 24
  • 25. Document standards q Document identification standards • How documents are uniquely identified. q Document structure standards • Standard structure for project documents. q Document presentation standards • Define fonts and styles, use of logos, etc. q Document update standards • Define how changes from previous versions are reflected in a document. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 25
  • 26. Document interchange standards q Interchange standards allow electronic documents to be exchanged, mailed, etc. q Documents are produced using different systems and on different computers. Even when standard tools are used, standards are needed to define conventions for their use e.g. use of style sheets and macros. q Need for archiving. The lifetime of word processing systems may be much less than the lifetime of the software being documented. An archiving standard may be defined to ensure that the document can be accessed in future. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 26
  • 27. Quality planning q A quality plan sets out the desired product qualities and how these are assessed and defines the most significant quality attributes. q The quality plan should define the quality assessment process. q It should set out which organisational standards should be applied and, where necessary, define new standards to be used. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 27
  • 28. Quality plans q Quality plan structure • Product introduction; • Product plans; • Process descriptions; • Quality goals; • Risks and risk management. q Quality plans should be short, succinct documents • If they are too long, no-one will read them. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 28
  • 29. Software quality attributes ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 29
  • 30. Quality control q This involves checking the software development process to ensure that procedures and standards are being followed. q There are two approaches to quality control • Quality reviews; • Automated software assessment and software measurement. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 30
  • 31. Quality reviews q This is the principal method of validating the quality of a process or of a product. q A group examines part or all of a process or system and its documentation to find potential problems. q 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). ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 31
  • 32. Types of review Review type Principal purpose Design or program To detect detailed errors in the requirements, design or code. A checklist of inspections possible errors should drive the review. Progress reviews To provide information for management about the overall progress of the project. This is b oth a process and a product review and is concerned with costs, plans and schedules. Quality reviews To carry out a t echnical analysis of product components or documentation to find mismatches between the specification and the component design, code or documentation and to ensure that defined quality standards have been followed. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 32
  • 33. Quality reviews q A group of people carefully examine part or all of a software system and its associated documentation. q Code, designs, specifications, test plans, standards, etc. can all be reviewed. q Software or documents may be 'signed off' at a review which signifies that progress to the next development stage has been approved by management. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 33
  • 34. Review functions q Quality function - they are part of the general quality management process. q Project management function - they provide information for project managers. q Training and communication function - product knowledge is passed between development team members. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 34
  • 35. Quality reviews q The objective is the discovery of system defects and inconsistencies. q Any documents produced in the process may be reviewed. q Review teams should be relatively small and reviews should be fairly short. q Records should always be maintained of quality reviews. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 35
  • 36. Review results q Comments made during the review should be 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; q Requirements and specification errors may have to be referred to the client. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 36
  • 37. Software measurement and metrics q Software measurement is concerned with deriving a numeric value for an attribute of a software product or process. q This allows for objective comparisons between techniques and processes. q Although some companies have introduced measurement programmes, most organisations still don’t make systematic use of software measurement. q There are few established standards in this area. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 37
  • 38. Software metric q Any type of measurement which relates to a software system, process or related documentation • Lines of code in a program, the Fog index, number of person-days required to develop a component. q Allow the software and the software process to be quantified. q May be used to predict product attributes or to control the software process. q Product metrics can be used for general predictions or to identify anomalous components. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 38
  • 39. Predictor and control metrics So ar e Softw arem e me pr od prPr oces Cont oledi meas emen ©Ian Sommerville 2004 Mana geme decis Software Engineering, 7th edition. Chapter 27 Slide 39
  • 40. Metrics assumptions q A software property can be measured. q 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. q This relationship has been formalised and validated. q It may be difficult to relate what can be measured to desirable external quality attributes. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 40
  • 41. Num oc e pr Internal and external attributes par am Mainta bilityin Cy clo tic e r Pr bilityxit Rliaoeer gor rco am ta thof P Leno o Num bility mes ge Usa us bilityua ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 41
  • 42. The measurement process q A software measurement process may be part of a quality control process. q Data collected during this process should be maintained as an organisational resource. q Once a measurement database has been established, comparisons across projects become possible. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 42
  • 43. Product measurement process Choose A measur ementsy an to Mea be m co Selec Ide compo ano beeem mea as comp char acte ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 43
  • 44. Data collection q A metrics programme should be based on a set of product and process data. q Data should be collected immediately (not in retrospect) and, if possible, automatically. q Three types of automatic data collection • Static product analysis; • Dynamic product analysis; • Process data collation. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 44
  • 45. Data accuracy q Don’t collect unnecessary data • The questions to be answered should be decided in advance and the required data identified. q Tell people why the data is being collected. • It should not be part of personnel evaluation. q Don’t rely on memory • Collect data when it is generated not after a project has finished. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 45
  • 46. Product metrics q A quality metric should be a predictor of product quality. q Classes of product metric • Dynamic 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 reliability; static metrics help assess complexity, understandability and maintainability. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 46
  • 47. Dynamic and static metrics q Dynamic metrics are closely related to software quality attributes • It is relatively easy to measure the response time of a system (performance attribute) or the number of failures (reliability attribute). q Static metrics have an indirect relationship with quality attributes • You need to try and derive a relationship between these metrics and properties such as complexity, understandability and maintainability. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 47
  • 48. Software product metrics Software metric Description Fan in/Fan-out Fan-in is a measure of the number of functions or methods that call some other 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 i s 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 m ay be high because of the complexity of the control logic needed to coordinate the called components. Length of code This 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. Cyclomatic complexity This is a m easure of the control complexity of a program. This control complexity may be related to program understandability. I discuss how to compute cyclomatic complexity in Chapter 22. Length of identifiers This is a measure of the average length of distinct identifiers in a p rogram. The longer the identifiers, the more likely they are to be m eaningful and hence the more understandable the program. Depth of conditional This is a measure of the depth of nesting of if-statements in a program. Deeply nested if nesting statements are hard to understand and are potentially error-prone. Fog index This is a measure of the average length of words and sentences in documents. The higher the value for the Fog index, the more difficult the document is to understand. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 48
  • 49. Object-oriented metrics Object-oriented Description metric Depth of inheritance This represents the number of discrete levels in the inheritance tree where sub- tree classes inherit attributes and operations (methods) from super-classes. The deeper the inheritance tree, the more complex the design. Many different object classes may have to be understood to understand the object classes at the leaves of the tree. Method fan-in/fan- This is directly related to fan-in and fan-out as described above and means out essentially the same thing. However, it may be appropriate to make a distinction between calls from other methods within the object and calls from external methods. Weighted methods This is the number of methods that are included in a class weighted by the per class 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 more difficult to understand. They may not be logically cohesive so cannot be reused effectively as super-classes in an inheritance tree. Number of This is the number of operations in a super-class that are over-ridden in a sub- overriding class. A high value for this metric indicates that the super-class used may not be operations an appropriate parent for the sub-class. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 49
  • 50. Measurement analysis q It is not always obvious what data means • Analysing collected data is very difficult. q Professional statisticians should be consulted if available. q Data analysis must take local circumstances into account. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 50
  • 51. Measurement surprises q Reducing the number of faults in a program leads to an increased number of help desk calls • The 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. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 51
  • 52. Key points q Software quality management is concerned with ensuring that software meets its required standards. q Quality assurance procedures should be documented in an organisational quality manual. q Software standards are an encapsulation of best practice. q Reviews are the most widely used approach for assessing software quality. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 52
  • 53. Key points q Software measurement gathers information about both the software process and the software product. q Product quality metrics should be used to identify potentially problematical components. q There are no standardised and universally applicable software metrics. ©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 27 Slide 53