Chapter 1 Introduction to Structured Design

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.

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.

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.

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.

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.

Design the New System  Computer-Assisted Software Engineering (CASE)  The automation of tools, methods, and procedures for system development.

Develop the New System  Each of the programs called for in the system design is constructed.  Program Development Cycle (PDC)

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.

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.

Program Flowchart and Pseudocode

Program Flowchart and Pseudocode cont.

Develop the New System  Hierarchy Chart or Structure Chart  Shows the relationships among parts of a program.  Each program part is called a module.

Structure Chart

Develop the New System  Class diagrams are expressed in the Unified Modeling Language, or UML.

Sample Input Screen (Not User Friendly)

Sample Input Screen (User- Friendly)

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.

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.

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.

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.

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.

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.

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.

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

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.

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

Structured Programming  IFTHENELSE Control Structure  The computer's ability to make a decision.

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

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.

Chapter 2 SIMPLE SEQUENCE Control Structure

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.

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.

Wake-Up Algorithm

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.

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).

Data Hierarchy

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.

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.

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.

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 algorithm—steps to be taken to solve the problem.

Sales Problem (Problem Flowchart)

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.

Sales Application Example  Memory Diagram:  Left is a list of all the variable names referenced.  Right represents the actual values.

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.

Sales Problem—Memory Diagram 2

Sales Problem—Memory Diagram 3

Sales Problem—Memory Diagram 4

Sales Application Example  Choose descriptive variable names.  Descriptive variable names make the algorithm much more self-documenting and easier to read.

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.