Chapter 20Quality AssuranceThrough Software Engineering.ppt

1、Chapter 20 Quality Assurance Through Software Engineering,Systems Analysis and Design Kendall and Kendall Fifth Edition,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-2,Major Topics,Quality assurance Walkthroughs Structure charts Modules Data and control passing Documentation Testing,Ken

2、dall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-3,Quality Assurance,Three quality assurance approaches through software engineering have been developed to evaluate the quality of the information systems design and analysis,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-4,Guidelin

3、es for Quality Software,Quality assurance approaches are Securing total quality assurance through designing systems and software with a top-down and modular approach Documenting software with appropriate tools Testing, maintaining, and auditing software,Kendall & Kendall,Copyright 2002 by Prentice H

4、all, Inc.,20-5,Total Quality Management,Total quality management (TQM) is a conception of quality as an evolutionary process toward perfection instead of conceiving quality as controlling the number of defective products produced The full organizational support of management and early commitment to

5、quality from the analyst and from the business are necessary,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-6,Structured Walkthroughs,One of the strongest quality assurance actions is structured walkthroughs Walkthroughs use peer reviewers to monitor the systems programming and overall d

6、evelopment They point out problems, and allow the programmer or analyst to make suitable changes,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-7,Personnel Involved in Structured Walkthroughs,Structured walkthroughs involve at least four people: The person responsible for the part of the

7、 system being reviewed A walkthrough coordinator A programmer or analyst peer A person to take notes about suggestions,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-8,Top-Down and Bottom-Up Approaches,The bottom-up approach and the top-down approach are available for quality system desi

8、gn,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-9,The Bottom-Up Approach,The bottom-up design refers to Identifying the processes that need computerization as they arise Analyzing them as systems Either coding them or purchasing packaged software to meet the immediate problem,Kendall &

9、 Kendall,Copyright 2002 by Prentice Hall, Inc.,20-10,Disadvantages of a Bottom-up Approach,The disadvantages of a bottom-up approach to design are There is a duplication of effort in purchasing software, and entering data Much worthless data are entered into the system Overall organizational objecti

10、ves are not considered and therefore cannot be met,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-11,The Top-Down Approach,Top-down design allows the systems analyst to ascertain overall organizational objectives along with ascertaining how they are best met in an overall system The syst

11、em is divided into subsystems and their requirements,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-12,Advantages of the Top-down Approach,The advantages of a top-down approach to design are Avoiding the chaos of attempting to design a system “all at once” The ability to have separate sy

12、stems analysis teams working in parallel on different but necessary subsystems Losing sight of system goals as a result of getting so mired in detail,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-13,Disadvantages of the Top-down Approach,The three disadvantages of a top-down approach ar

13、e There is a danger that the system will be divided into the wrong subsystems Once subsystem divisions are made, their interfaces may be neglected or ignored The subsystems must be reintegrated, eventually,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-14,Modular Programming and the Top-

14、Down Approach,The modular programming concept is useful for a top-down approach Once the top-down design approach is taken, the whole system is broken into logical, manageable sized modules, or subprograms to use modular programming techniques,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,

15、20-15,Advantages of Modular Programming,Advantages of modular programming Modules are easier to write and debug Tracing an error in a module is less complicated Modules are easier to maintain Modules are easier to grasp because they are self-contained subsystems,Kendall & Kendall,Copyright 2002 by P

16、rentice Hall, Inc.,20-16,Guidelines for Modular Programming,Four guidelines for correct modular programming are Keep each module to a manageable size Pay particular attention to the critical interfaces Minimize the number of modules the user needs to modify when making changes Maintain the hierarchi

17、cal relationships set up in the top-down phases,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-17,Linking Programs in Microsoft Windows,There are two systems to link programs in Microsoft Windows: Dynamic Data Exchange (DDE) updates data in one program based on data in another program Ob

18、ject Linking and Embedding (OLE) where an object in a second program retains the properties of an object in the first program,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-18,Structure Charts,The recommended tool for designing a modular, top-down system is a structure chart They help sy

19、stems analysts by providing a picture of modules and the relationships among those modules A diagram consisting of rectangular boxes that represents the modules Connecting lines or arrows,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-19,Objectives of a Structure Chart,The objectives of

20、a structure chart are To encourage a top-down design To support the concept of modules and identify the appropriate modules To identify and limit as much as possible the data couples and control flags that pass between modules,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-20,Data and Co

21、ntrol Passing,Data and control passed between structure chart modules is either Data coupling, only the data required by the module are passed, or Stamp coupling, more data than necessary are passed between the modules Control coupling,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-21,Co

22、ntrol Coupling,Control coupling is passing: Switches, which have only two values, and Flags, which have more than two values,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-22,Control Coupling,Control flags should be passed up the structure chart Control modules make the decisions about w

23、hich lower-level modules should be executed Lower-level modules are functional, performing only one task,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-23,Minimal Coupling,Systems analysts should keep the number of couples to a minimum The fewer data couples and control flags one has in

24、the system, the easier it is to change the system,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-24,Transform and Transaction Centered Design,There are two approaches to structure chart design: Transform-centered structure charts are used when all the transactions follow the same path Tr

25、ansaction-centered structure charts are used when all the transactions do not follow the same path,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-25,Data Flow Diagrams and Structure Charts,A data flow diagram may be used to create a structure chart in the following two ways: Indicating t

26、he sequence of the modules Indicating modules subordinate to a higher module,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-26,Types of Modules,Modules fall into three classes: Control modules, determining the overall program logic Transformational modules, changing input into output Spe

27、cialized modules, performing detailed, functional work,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-27,Improper Subordination,A subordinate module is one found lower on the structure chart, called by another higher module Allowing a lower-level module to perform any function of the cal

28、ling, higher-level module, is called improper subordination,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-28,System Documentation,One of the requirements for total quality assurance is preparation of an effective set of system documentation This serves as A guideline for users A communi

29、cation tool A maintenance reference as well as development reference,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-29,Forms of System Documentation,Documentation can be one of the following: Nassi-Schneiderman charts Pseudocode Procedure manuals The FOLKLORE method,Kendall & Kendall,Cop

30、yright 2002 by Prentice Hall, Inc.,20-30,Advantages of Nassi-Schneiderman Charts,The main advantages of Nassi-Schneiderman charts are They adopt the philosophy of structured programming They use a limited number of symbols so that the N-S charts are easier to draw and understand,Kendall & Kendall,Co

31、pyright 2002 by Prentice Hall, Inc.,20-31,Pseudocode,Pseudocode is an English-like code to represent the outline or logic of a program It is not a particular type of programming code, but it can be used as an intermediate step for developing program code It does not have strict syntax rules,Kendall

32、& Kendall,Copyright 2002 by Prentice Hall, Inc.,20-32,Procedure Manuals,The biggest complaints with procedure manuals are that They are poorly organized It is difficult to find needed information The specific case in question does not appear in the manual The manual is not written in plain English,K

33、endall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-33,FOLKLORE,The FOLKLORE documentation method collects information in the categories of Customs Tales Sayings Art forms,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-34,Web Documentation,A Web site can help maintain and document

34、the system by providing FAQ (Frequently Asked Questions) Help desks Technical support Fax-back services Some Web sites have a question-and-answer approach for providing help,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-35,Choosing a Documentation Technique,Guidelines for choosing a doc

35、umentation technique: Is compatible with existing documentation Is understood by others in the organization Does it allow you to return to working on the system after you have been away from it for a period of time,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-36,Choosing a Documentatio

36、n Technique,Further guidelines Is it suitable for the size of the system you are working on? Does it allow for a structured design approach if it is considered to be more important than other factors? Does it allow for easy modification?,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-37,

37、Code Generation and Design Reengineering,Code generation uses the CASE design information to create or generate all or part of the computer source program code Design reengineering, or reverse engineering, allows the analyst to create CASE design entities from existing computer source code,Kendall &

38、 Kendall,Copyright 2002 by Prentice Hall, Inc.,20-38,Code Generation and Design Reengineering Advantages,The advantages of code generation and design reengineering are Documentation is produced for the programs The generated code does not contain any software “bugs” The regenerated code may be in a

39、newer version of the compiler language Unused code may be easily removed,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-39,Testing Overview,The new or modified application programs, procedural manuals, new hardware, and all system interfaces must be tested thoroughly,Kendall & Kendall,Co

40、pyright 2002 by Prentice Hall, Inc.,20-40,Testing Procedures,The following testing process is recommended: Program testing with test data Link testing with test data Full system testing with test data Full system testing with live data,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-41,Pr

41、ogram Testing with Test Data,Desk check programs Test with valid and invalid data Check for errors and modify programs,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-42,Link Testing with Test Data,Also called string testing See if programs can work together within a system Test for norma

42、l transactions Test with invalid data,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-43,Full System Testing with Test Data,Operators and end users test the system Factors to consider Is adequate documentation available? Are procedure manuals clear? Do work flows actually flow? Is output

43、correct and do the users understand the output?,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-44,Full System Testing with Live Data,Compare the new system output with the existing system output Only a small amount of live data are used,Kendall & Kendall,Copyright 2002 by Prentice Hall,

44、Inc.,20-45,Maintenance,Maintenance is due to Errors or flaws in the system Enhancing the system Feedback procedures must be in place to communicate suggestions,Kendall & Kendall,Copyright 2002 by Prentice Hall, Inc.,20-46,Auditing,There are internal and external auditors Internal auditors study the controls used in the system to make sure that they are adequate Internal auditors check security controls External auditors are used when the system influences a companys financial statements,