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CS605 - Software Engineering II - Lecture Handout 27

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Software Quality Assurance

Quality cannot be assured without first understanding its nature and characteristics. So the first question one has to ask is: what is quality?

Software quality is defined as conformance to explicitly stated functional and non-functional requirements, explicitly documented development standards, and implicit characteristics that are expected of all professionally developed software.

This definition emphasizes upon three important points:

    • Software requirements are the foundation from which quality is measured. Lack of conformance is lack of quality
    • Specified standards define a set of development criteria that guide the manner in which software is engineered. If the criteria are not followed, lack of quality will almost surely result.
    • A set of implicit requirements often goes unmentioned (ease of use, good maintainability etc.)
    Another very important question is: Do you need to worry about it after the code has been generated? In fact, SQA is an umbrella activity that is applied throughout the software process.

    Also, do we care about internal quality or the external quality? And finally, is there a relationship between internal and external qualities? That is, does internal quality translate in external quality?

    In the literature, quality has been defined through in many different manners. One group believes that the quality has measurable characteristic such as cyclomatic complexity, cohesion, and coupling.
    We can then talk about quality from different aspects. Quality of design tries to determine the quality of design related documents including requirements, specifications, and design. Quality of conformance looks at the implementation and if it follows the design then the resulting system meets its goals then conformance quality is high.
    Are there any other issues that need to be considered? Glass defines quality as a measure of  user satisfaction which is defined by
    compliant product + good quality + delivery within budget and schedule

    DeMarco defines product quality as a function of how much it changes the world for the better.

    So, there are many different way to look at the quality.

    Quality Assurance

    Goal of quality assurance is to provide the management with the necessary data to be informed about product quality. It consists of auditing and reporting functions of management. If data provided through QA identifies problems, the management deploys the necessary resources to fix it and hence achieves desired quality control.

    Cost of quality

    A very significant question is: does quality assurance add any value. That is, is worth spending a lot of money in quality assurance practices? In order to understand the impact of quality assurance practices, we have to understand the cost of quality (or lack thereof) in a system.
    Quality has a direct and indirect cost in the form of cost of prevention, appraisal, and failure.
    If we try to prevent problems, obviously we will have to incur cost. This cost includes:

      • Quality planning
      • Formal technical reviews
      • Test equipment
      • Training

      We will discuss these in more detail in the later sections.
      The cost of appraisal includes activities to gain insight into the product condition. It involves in-process and inter-process inspection and testing.
      And finally, failure cost. Failure cost has two components: internal failure cost and external failure cost. Internal failure cost requires rework, repair, and failure mode analysis. On the other hand, external failure cost involves cost for complaint resolution, product return and replacement, help-line support, warranty work, and law suits.
      It is trivial to see that cost increases as we go from prevention to detection to internal failure to external failure. This is demonstrated with the help of the following example:
      Let us assume that a total of 7053 hours were spent inspecting 200,000 lines of code with the result that 3112 potential defects were prevented. Assuming a programmer cost of $40 per hour, the total cost of preventing 3112 defects was $382,120, or roughly $91 per defect.
      Let us now compare these numbers to the cost of defect removal once the product has been shipped to the customer. Suppose that there had been no inspections, and the programmers had been extra careful and only one defect one 1000 lines escaped into the product shipment. That would mean that 200 defects would still have to be fixed in the field. As an estimated cost of $25000 per fix, the cost would be $5 Million or approximately 18 times more expensive than the total cost of defect prevention

      That means, quality translates to cost savings and an improved bottom line.

      SQA Activities

      There are two different groups involved in SQA related activities:

        • Software engineers who do the technical work
        • SQA group who is responsible for QA planning, oversight, record keeping, analysis, and reporting
        Software engineers address quality by applying solid technical methods and measures, conducting formal and technical reviews, and performing well planned software testing. The SQA group assists the software team in achieving a high quality product.

        SQA Group Activities

        An SQA plan is developed for the project during project planning and is reviewed by all stake holders. The plan includes the identification of:

        • Evaluations to be performed
        • Audits and reviewed to be performed
        • Standards that are applicable to the project
        • Procedures for error reporting and tracking
        • Documents to be produced by the SQA group
        • Amount of feedback provided to the software project team

        The group participates in the development of the project’s software process description. The software team selects the process and SQA group reviews the process description for compliance with the organizational policies, internal software standards, externally imposed standards, and other parts of the software project plan.
        The SQA group also reviews software engineering activities to verify compliance with the defined software process. It identifies, documents, and tracks deviations from the process and verifies that the corrections have been made. In addition, it audits designated software work products to verify compliance with those defined as part of the software process. It, reviews selected work products, identifies, documents, and tracks deviations; verifies that corrections have been made; and reports the results of its work to the project manager.
        The basis purpose is to ensure that deviations in software work and work products are documented and handled according to documented procedures. These deviations may be encountered in the project plan, process description, applicable standards, or technical work products. The group records any non-compliance and reports to senior management and non-compliant items are recorded and tracked until they are resolved.
        Another very important role of the group is to coordinate the control and management of change and help to collect and analyze software metrics.

        Quality Control

        The next question that we need to ask is, once we have defined how to assess quality, how are we going to make sure that our processes deliver the product with the desired quality. That is, how are we going to control the quality of the product?
        The basic principle of quality control is to control the variation as variation control is the heart of quality control. It includes resource and time estimation, test coverage, variation in number of bugs, and variation in support.
        From one project to another we want to minimize the predicted resources needed to complete a project and calendar time. This involves a series of inspection, reviews, and tests and includes feedback loop. So quality control is a combination of measurement and feedback and combination of automated tools and manual interaction.