Quality Management Ian Sommerville 2006 Software Engineering,

Quality Management Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 1

Objectives To introduce the quality management process and key quality management activities To explain the role of standards in quality management To explain the concept of a software metric, predictor metrics and control metrics To explain how measurement may be used in assessing software quality and the limitations of software measurement Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 2

Topics covered Process and product quality Quality assurance and standards Quality planning Quality control Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 3

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. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 4

What is quality? Quality, simplistically, means that a product should meet its specification. 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 2006 Software Engineering, 8th edition. Chapter 27 Slide 5

The quality compromise We cannot wait for specifications to improve before paying attention to quality management. We must put quality management procedures into place to improve quality in spite of imperfect specification. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 6

Scope of quality management 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. For smaller systems, quality management needs less documentation and should focus on establishing a quality culture. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 7

Quality management activities Quality assurance Quality planning Select applicable procedures and standards for a particular project and modify these as required. Quality control Establish organisational procedures and standards for quality. Ensure that procedures and standards are followed by the software development team. Quality management should be separate from project management to ensure independence. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 8

Quality management and software development Software development process D1 D2 D3 D4 D5 Quality management process Standards and procedures Ian Sommerville 2006 Quality plan Quality review repor ts Software Engineering, 8th edition. Chapter 27 Slide 9

Process and product quality The 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. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 10

Process-based quality There is a straightforward link between process and product in manufactured goods. 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. Care must be taken not to impose inappropriate process standards - these could reduce rather than improve the product quality. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 11

Process-based quality Define pr ocess Develop product Improve process Ian Sommerville 2006 Assess pr oduct quality No Quality OK Yes Software Engineering, 8th edition. Chapter 27 Standar dise process Slide 12

Practical process quality Define process standards such as how reviews should be conducted, configuration management, etc. Monitor the development process to ensure that standards are being followed. Report on the process to project management and software procurer. Don’t use inappropriate practices simply because standards have been established. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 13

Quality assurance and standards Standards are the key to effective quality management. They may be international, national, organizational or project standards. Product standards define characteristics that all components should exhibit e.g. a common programming style. Process standards define how the software process should be enacted. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 14

Importance of standards Encapsulation of best practice- avoids repetition of past mistakes. They are a framework for quality assurance processes - they involve checking compliance to standards. They provide continuity - new staff can understand the organisation by understanding the standards that are used. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 15

Product and process standards Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 16

Problems with standards They may not be seen as relevant and up-todate by software engineers. They often involve too much bureaucratic form filling. If they are unsupported by software tools, tedious manual work is often involved to maintain the documentation associated with the standards. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 17

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. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 18

ISO 9000 An international set of standards for quality management. Applicable to a range of organisations from manufacturing to service industries. ISO 9001 applicable to organisations which design, develop and maintain products. ISO 9001 is a generic model of the quality process that must be instantiated for each organisation using the standard. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 19

ISO 9001 Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 20

ISO 9000 certification Quality 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. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 21

ISO 9000 and quality management ISO 9000 quality models instantiated as Organisation quality man ual documents is used to de velop Project 1 quality plan Project 2 quality plan Organisation quality pr ocess instantiated as Project 3 quality plan Project quality management Supports Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 22

Documentation standards Particularly important - documents are the tangible manifestation of the software. Documentation process standards Document standards Concerned with how documents should be developed, validated and maintained. Concerned with document contents, structure, and appearance. Document interchange standards Concerned with the compatibility of electronic documents. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 23

Documentation process Create initial draft Stage 1: Creation Proofread text Stage 2: Polishing Layout text Incorporate review comments Review draft Re-draft document Approved document Produce final draft Check final draft Approved document Review layout Produce print masters Print copies Stage 3: Production Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 24

Document standards Document identification standards Document structure standards Standard structure for project documents. Document presentation standards How documents are uniquely identified. Define fonts and styles, use of logos, etc. Document update standards Define how changes from previous versions are reflected in a document. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 25

Document interchange standards Interchange standards allow electronic documents to be exchanged, mailed, etc. 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. 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 2006 Software Engineering, 8th edition. Chapter 27 Slide 26

Quality planning A 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. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 27

Quality plans Quality plan structure Product introduction; Product plans; Process descriptions; Quality goals; Risks and risk management. Quality plans should be short, succinct documents If they are too long, no-one will read them. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 28

Software quality attributes Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 29

Quality control This involves checking the software development process to ensure that procedures and standards are being followed. There are two approaches to quality control Quality reviews; Automated software assessment and software measurement. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 30

Quality reviews This is the principal method of validating the quality of a process or of a product. A group examines 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). Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 31

Types of review Review type Principal purpose Design or program inspections To detect detailed errors in the requirements, design or code. A checklist of 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 2006 Software Engineering, 8th edition. Chapter 27 Slide 32

Quality reviews A 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. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 33

Review functions Quality function - they are part of the general quality management process. Project management function - they provide information for project managers. Training and communication function product knowledge is passed between development team members. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 34

Quality reviews The 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. Records should always be maintained of quality reviews. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 35

Review results 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; Requirements and specification errors may have to be referred to the client. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 36

Software measurement and metrics Software 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. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 37

Software metric 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. 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. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 38

Predictor and control metrics Software process Software product Control measurements Predictor measur ements Management decisions Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 39

Metrics assumptions A 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. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 40

Internal and external attributes Number ofprocedure parameters Maintainability Cyclomatic complexity Reliability Program size in lines of code Portability Number of error messages Usability Length of user man ual Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 41

The measurement process A software measurement process may be part of a quality control process. Data collected during this process should be maintained as an organisational resource. Once a measurement database has been established, comparisons across projects become possible. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 42

Product measurement process Choose measurements to be made Analyse anomalous components Select components to be assessed Identify anomalous measur ements Measure component characteristics Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 43

Data collection A metrics programme should be based on a set of product and process data. Data should be collected immediately (not in retrospect) and, if possible, automatically. Three types of automatic data collection Static product analysis; Dynamic product analysis; Process data collation. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 44

Data accuracy Don’t collect unnecessary data Tell people why the data is being collected. The questions to be answered should be decided in advance and the required data identified. It should not be part of personnel evaluation. Don’t rely on memory Collect data when it is generated not after a project has finished. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 45

Product metrics A quality metric should be a predictor of product quality. 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 2006 Software Engineering, 8th edition. Chapter 27 Slide 46

Dynamic and static metrics 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). 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 2006 Software Engineering, 8th 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 errorproneness in components. Cyclomatic complexity This is a m easure of the control complexity of a p rogram. 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 nesting This is a measure of the depth of nesting of if-statements in a program. Deeply nested if 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 2006 Software Engineering, 8th edition. Chapter 27 Slide 48

Object-oriented metrics Object-oriented metric Description Depth of inheritance tree This represents the number of discrete levels in the inheritance tree where subclasses 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/fanout This is directly related to fan-in and fan-out as described above and means 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 per class This is the number of methods that are included in a 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 more difficult to understand. They may not be logically cohesive so cannot be reused effectively as super-classes in an inheritance tree. Number of overriding operations This is the number of operations in a super-class that are over-ridden in a subclass. A high value for this metric indicates that the super-class used may not be an appropriate parent for the sub-class. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 49

Measurement analysis It is not always obvious what data means Analysing collected data is very difficult. Professional statisticians should be consulted if available. Data analysis must take local circumstances into account. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 50

Measurement surprises 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 2006 Software Engineering, 8th edition. Chapter 27 Slide 51

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. Software standards are an encapsulation of best practice. Reviews are the most widely used approach for assessing software quality. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 52

Key points Software measurement gathers information about both the software process and the software product. Product quality metrics should be used to identify potentially problematical components. There are no standardised and universally applicable software metrics. Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 27 Slide 53