Introduction to Structured Design

1
Chapter 1

• Introduction to Structured Design

2
Introduction

• System
• A combination of people, equipment, and
  procedures that work together to perform a
  specific function.
• Manually operated
• Computer assisted
• Computer-Based Information System
• A system in which some of the procedures are
  performed by a computer.

3
System Development Life Cycle

• System Development Life Cycle (SDLC)
• A series of well-designed steps that should be
  followed when a system is created or changed.

4
Analyze the Current System

• System Analysts
• Study every aspect of the existing system to get
  a clear understanding of what things are done and
  how.
• Identifies any problems associated with the
  system.
• Most effective technique is to talk to users of
  the system.
• Users
• People who are directly involved with the system
  in their day-today activities.

5
Define the New System Requirements

• Specify what needs to be done, not how to do it.
• Which changes are necessary to eliminate the
  problems identified in the initial analysis.
• After the analyst works out all the requirements,
  prepare a report outlining these requirements for
  management.

6
Design the New System

• System Designer
• uses the requirements defined in the preceding
  step as a basis for designing the new or modified
  system.
• System Flowchart
• shows all the major inputs and outputs.
• No detail is given as to how the program actually
  works.

7
Design the New System

• Computer-Assisted Software Engineering (CASE)
• The automation of tools, methods, and procedures
  for system development.

8
Develop the New System

• Each of the programs called for in the system
  design is constructed.
• Program Development Cycle (PDC)

9
Develop the New System

• Review the Program Requirements
• If anything is unclear at this point, the
  programmer asks for more information from the
  system analyst who wrote the original
  requirement, from the system designer, or even
  from a future user of the program.

10
Develop the New System

• Develop the Program Logic
• The actual processing steps within each program
  in the system are developed.
• Two common tools
• Program flowcharts
• Use symbols graphically depict the
  problem-solving logic within a program.
• Pseudocode
• Use English-language statements that describe the
  processing steps.

11
Program Flowchart and Pseudocode
12
Program Flowchart and Pseudocode cont.
13
Develop the New System

• Hierarchy Chart or Structure Chart
• Shows the relationships among parts of a program.
• Each program part is called a module.

14
Structure Chart
15
Develop the New System

• Class diagrams are expressed in the Unified
  Modeling Language, or UML.

16
Sample Input Screen (Not User Friendly)
17
Sample Input Screen (User-Friendly)
18
Develop the New System

• Graphical User Interface (GUI)
• Presents information in an easy-to-use
  point-and-click fashion.
• A programmer must be able to understand the steps
  in the design if modifications are required.
• The person modifying the program may not be the
  one who wrote it originally.
• The program logic must be clear and easy to
  follow.

19
Develop the New System

• Write the Program.
• Procedure-oriented languages
• Focus on the specific steps in the
  problem-solving process.
• Fourth-generation languages (4GLs) has become
  common.
• Nonprocedural languages defines what needs to be
  done, not how.
• Packages contain programming statements that can
  be used alone or in combination (macros and
  programs) to accomplish a task more efficiently.

20
Develop the New System

• Event-driven program
• Designed to respond to actions that occur when
  the program is executing.
• The actions can be initiated by the computer or
  by a user.
• Object-oriented languages
• Deal with classes and objects, which are
  instances of those classes.
• Java and C
• CASE tools include basic tutorials and online
  help systems designed to help users, analyst,
  designers, and programmers use the applications
  and tools effectively.

21
Develop the New System

• Test and Debug the Program
• Check for errors (bugs) and test with sample data
  to see if actual results match expected results.
• Syntax errors
• The programmer does not follow the language
  rules.
• Logic error
• Occurs when a step in the program logic is
  incorrect.
• Every possible condition should be tested if
  feasible.
• Needs to be designed to handle invalid input data.

22
Develop the New System

• Unit Testing
• Programs, modules, or classes that make up a
  system should first be tested individually.
• System Testing, or Integration
• Programs, modules, or classes should be tested
  together as a system.

23
Develop the New System

• Complete the Program Documentation
• Documentation occurs throughout the program
  development cycle.
• Technical reference needs to be created.
• User guides need to be created.
• Good documentation cannot be overemphasized in
  its importance.

24
Develop the New System

• Implement the New System
• Users are trained, and operating procedures are
  defined.
• System documentation is reviewed, revised as
  necessary, and prepared in its final form.
• New systems may be run concurrently with the
  existing (old) systems the new system may
  completely replace the old system or the new
  system may be phased in gradually.

25
Develop the New System

• Evaluate the New System
• Is it meeting the required objectives?
• Parts of the system may have to be modified.

26
Structured Programming

• Structured programming
• A technique that has proven to be very effective
  in solving problems as well as in modifying
  solutions.
• Control structures
• The ability to express a problem solution using
  only three basic patterns of logic.
• A paper by C. Bohm and B. Jacopini, in 1965, is
  proof that the three structures are sufficient
  for programming.

27
Structured Programming

• Basic Control Structures
• SIMPLE SEQUENCE Control Structure
• Execute instructions in a step-by-step,
  sequential manner.

28
Structured Programming

• IFTHENELSE Control Structure
• The computer's ability to make a decision.

29
Structured Programming

• DOWHILE Control Structure
• The computer's ability to repeat a series of
  instructions.
• A series of repeated instructions is a loop.

30
Structured Programming

• Infinite Loop - there is no way out.
• Every loop must include a statement that defines
  how many times to execute the loop steps or under
  what condition to continue or to stop the looping
  process.

31
Chapter 2

• SIMPLE SEQUENCE
• Control Structure

32
Introduction

• Algorithm
• A step-by-step procedure to solve a problem.
• Requirements
• Use operations from only a given set of basic
  operations.
• Produce the problem solution, or answer, in a
  finite number of such operations.

33
Introduction

• Program Flowchart
• Rectangles represent the process symbol.
• Ellipse symbols are called terminal interrupt
  symbols.
• All symbols are connected by flowlines.
• Arrowheads show the direction of the flow.

34
Wake-Up Algorithm
35
Introduction

• Information Processing
• Another name for paperwork.
• A series of planned actions and operations upon
  data to achieve a desired result.
• Information-processing system elements
• The source data, or input, entering the system.
• The orderly, planned processing within the
  system.
• The end result, or output, from the system.

36
Data Hierarchy

• Data Hierarchy
• FILE
• A collection of related data or facts.
• RECORD
• A collection of data, about a single entity in
  the file.
• FIELD
• Any single piece of data, about an entity
  (record) in a file.
• CHARACTER
• A letter (A-Z, a-z), number (0-9), or special
  character ( . or ? or , and so on).

37
Data Hierarchy
38
Sales Application Example

• The sales operations of a large department store.
• A system flowchart is often created to show more
  general information about the application.

39
Sales Application Example

• The leftmost symbol is the general input/output
  (I/O) symbol, the parallelogram.
• The rectangular symbol is a general-purpose
  symbol indicating, collectively, all processing
  steps within the sales program.
• Represents an action or series of actions
  performed with computer help.
• Flowcharts aid in problem analysis and solution
  planning.

40
Sales Application Example

• The American National Standards Institute (ANSI)
  coordinated the development of a standard set of
  flowcharting symbols and associated meanings.
• A system flowchart shows the data, flow of work,
  and workstations within an information-processing
  system.

41
Sales Application Example

• Sales Application Program Flowchart
• In the program flowchart, the detailed steps
  needed to process the data about one person's
  sales must be specified.
• To major actions with any problem-solving task
• Define the problem to be solved.
• Develop a solution algorithmsteps to be taken to
  solve the problem.

42
Sales Problem (Problem Flowchart)
43
Sales Application Example

• Variables
• Data items whose values may change, or vary,
  during processing.
• Defined Value
• When a variable is used in conjunction with a
  READ statement, we can assume that the value of
  the variable is now known to the computer.
• Data Independence
• The program will perform the required processing
  steps on any set of input data.

44
Sales Application Example

• Memory Diagram
• Left is a list of all the variable names
  referenced.
• Right represents the actual values.

45
Sales Application Example

• Assignment Statement
• Only a single variable name may appear to the
  left of the assignment symbol, which in our
  example is .
• Only a single variable name, constant, or
  expression may appear to the right of the .
• Everything to the right of the must be known
  (defined) to the computer.
• Constant
• A value that never changes.

46
Sales ProblemMemory Diagram 2
47
Sales ProblemMemory Diagram 3
48
Sales ProblemMemory Diagram 4
49
Sales Application Example

• Choose descriptive variable names.
• Descriptive variable names make the algorithm
  much more self-documenting and easier to read.

50
Design Verification

• The solution algorithm should be verified.
• Prevent errors from occurring.
• Detect and eliminate errors as soon as possible.
• A program can be written correctly, so that it
  executes properly the first time it is run.
• Careful, early verification of the program
  design, or solution algorithm, is an essential
  step in achieving this objective.