Ppt qc

Ppt qc

• 2.
   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
• 3.
   Process andproduct quality  Quality assurance and standards  Quality planning  Quality control
• 4.
   Concerned withensuring 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.
• 5.
   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.
• 6.
   We cannotwait 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.
• 7.
   Quality managementis 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.
• 8.
   Quality assurance ◦ Establish organisational procedures and standards for quality.  Quality planning ◦ Select applicable procedures and standards for a particular project and modify these as required.  Quality control ◦ Ensure that procedures and standards are followed by the software development team.  Quality management should be separate from project management to ensure independence.
• 9.
  Software development process D1 D2 D3 D4 D5 Quality m anagement process Standards and Quality Quality review repor ts procedures plan
• 10.
   The qualityof 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.
• 11.
   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.
• 12.
  Develop Assess pr oduct Define process product quality No Y es Improve Quality Standar dis e process OK process
• 13.
   Define processstandards 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.
• 14.
   Standards arethe 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.
• 15.
   Encapsulation ofbest 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.
• 17.
   They maynot 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 manual work is often involved to maintain the documentation associated with the standards.
• 18.
   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.
• 19.
   Particularly important - documents are the tangible manifestation of the software.  Documentation process standards ◦ Concerned with how documents should be developed, validated and maintained.  Document standards ◦ Concerned with document contents, structure, and appearance.  Document interchange standards ◦ Concerned with the compatibility of electronic documents.
• 20.
  Incorporate Crea te Review Re-draft review initial dr aft draft docum ent comm ents Stage 1: Creation Appr oved document Proofread Produce Check text final dr aft final dr aft Stage 2: Polishing Appr oved document Layout Review Produce Print text layout print masters copies Stage 3: Production
• 21.
   Document identification standards ◦ How documents are uniquely identified.  Document structure standards ◦ Standard structure for project documents.  Document presentation standards ◦ Define fonts and styles, use of logos, etc.  Document update standards ◦ Define how changes from previous versions are reflected in a document.
• 22.
   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.
• 23.
   A qualityplan 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.
• 24.
   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.
• 26.
   This involveschecking 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.
• 27.
   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).
• 28.
  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.
• 29.
   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.
• 30.
   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.
• 31.
   The objectiveis 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.
• 32.
   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.
• 33.
   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.
• 34.
   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.
• 35.
  Softw are Softw are process product Contr ol Predictor measur ements measur ements Mana gement decisions
• 36.
   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.
• 37.
  Number of procedure par ameters Maintaina bility Cyclomatic comple xity Relia bility Prog ram siz e in lines of code Por tability Number of error messa ges Usability Length of user man ual
• 38.
   A softwaremeasurement 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.
• 39.
  Choose Analy se measur ements anomalous to be made com ponents Select Identify components to anomalous be assessed measur ements Measur e component characteristics
• 40.
   A metricsprogramme 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.
• 41.
   Don’t collect unnecessary data ◦ The questions to be answered should be decided in advance and the required data identified.  Tell people why the data is being collected. ◦ 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.
• 42.
   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.
• 43.
   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.
• 44.
  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 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 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.
• 45.
  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.
• 46.
   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.
• 47.
   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.
• 48.
   Software qualitymanagement 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.
• 49.
   Software measurementgathers 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.