PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 1 Key Definitions Program design is the part of the design phase during which analysts create instructions for the programmers about how code needs to be written and how pieces of code need to fit together to form a program. The top-down modular approach begins with understanding the “big picture” and organizing it into discreet and understandable smaller pieces.

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 2 The Top-Down Modular Approach

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 3 Structure Chart

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 4 The Structure Chart Shows all components of code in a hierarchical format Sequence Selection Iteration

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 5 Structure Chart Elements

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 6 Revised Structure Chart Example

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 7 Building the Structure Chart Processes in the DFD tend to represent one module on the structure chart The DFD levelling can correspond to the structure chart hierarchy

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 8 Steps in Building the Structure Chart 1. Identify top level modules and decompose them into lower levels 2. Add control connections 3. Add couples 4. Review and revise again and again until complete

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 9 Typical Structures Transaction structures Control modules that send work to subordinates for various processing work Often one inflow and several outflows on DFD Transform structure Modules that work together to perform a task Often one inflow that is changed into another sort of outflow on DFD

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 10 Transaction Structure

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved.

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved.

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved.

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved.

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved.

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 16 Design Guidelines High quality structure charts result in programs that are modular, reusable and easy to implement. Measures include: Cohesion Coupling Appropriate levels of fan-in and fan-out

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 17 Types of Cohesion Functional Sequential Communicational Procedural Temporal Logical Coincidental What Would Be an Example of Each?

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 18 Example of Low Cohesion

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 19 Cohesion Decision Tree Adapted from Page-Jones, 1980

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 20 Factoring Separates tasks into different modules Reduces use of control flags

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 21 Types of Coupling Data Stamp Control Common Content What Would Be an Example of Each?

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 22 Examples of Fan-in and Fan- out

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 23 Quality Checklist 1. Library modules have been created where ever possible 2. The diagram has a high fan-in structure 3. Control modules have no more than 7 subordinates 4. Each module performs only one function (high cohesion) 5. Modules sparingly share information (loose coupling) 6. Data couples that are passed are actually used by the accepting module 7. Control couples are passed from “low to high” 8. Each module has a reasonable amount of code associated with it

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 24 Program Specification

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 25 Program Specifications Content No standard approach Include program information Note events that trigger actions List inputs and outputs Include pseudocode Present additional notes and comments

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 26 Program Specification Form

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 27 Pseudocode Example (Get CD-info module) Accept (CD_title) {Required} Accept (CD_artist) {Required} Accept (CD_category) {Required} Accept (CD_length) Return

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved.

PowerPoint Presentation for Dennis & Haley Wixom, Systems Analysis and Design Copyright 2000 © John Wiley & Sons, Inc. All rights reserved. Slide 29 Summary The structure chart shows all of the functional components needed in the program at a high level. Components of the structure chart show sequence, selection, and iteration Follow design guidelines regarding cohesion, coupling, and fan-in/fan-out. Prepare detailed specifications to programmers including pseudocode to show important programming structures.