Chapter 2 - Taking a Structured Approach and Using Modeling Tools

A) Taking a Structured Approach to Developing Systems (Fig. 2.1)

goal:

• 1) meets user requirements,
• 2) on time & within budget,
• 3) is easy to work with, understand and maintain

1. modeling tools - used to model & describe systems
2. modularization - divide system into indepentently operable modules
   • simplifies design
   • reduces errors
   • easier to test
   • turnover of project team members has less impact
   • easier to optimize
   • reusablity of modules
3. top-down decomposition
4. iteration
5. parallel activities
6. automated systems development (CASE)

B) Roles and Types of Modeling Tools

• Communications
• Experimentation
• Prediction

Questions to ask about modeling tools:

1. Is it easy to understand?
2. Is it an aid to clear thinking?
3. Does it help communicate the design of a current or new system?
4. Does it assist in experimentation with new ideas?
5. Does it encourage good systems design?
6. Could it be used to help redict actual functioning of new system?
7. Does it help structure the SAD phases?

Types of Modeling Tools

• Data flow diagrams (DFD)
• Data dictionary
• Entity relationship diagrams (ERD)
• State transition diagrams
• Structure chart
• Structured program flowchart
• Process specification charts
• Warnier-Orr diagram (WOD)
• Jackson diagrams

C) Creating a Data Flow Diagram (Fig. 2.2)

Steps in preparing DFDs (Fig. 6.3)

1. Draw a Context-Level Diagram (Fig. 6.4)
2. Decompose the Context-Level Diagram
3. Decompose to an Elementary Level(Student Housing System)

D) Using a Data Dictionary for Systems Analysis

• Student-Record = Student-Name + Student-Home-Address + Campus-Address + ...
• Campus-Address = Dorm-Name + Floor + Room-Nbr

E) Creating an Entity Relationship Diagram (Fig. 2.5)

• model data stores in DFD
• steps in preparing ERDs (Fig. 2.6)
• Identify Entities
• Indicate Relationships Between Entities
• Define Keys for Each Entity
• Define and Map Data Elements for Each Entity (Fig. 2.7)
• Normalize the Data Model

F) Creating a State Transition Diagram (STD) (Fig. 2.8)

• identify all possible states for the system
• identify activities that cause a transition from one state to another (Fig. 2.9)

G) Creating a Structure Chart

models the software that support the system (Fig. 2.11)

steps in preparing structure charts

1. identify the central transform
2. produce a "first-cut" structure chart
3. add modules and show data flows
4. write module details
5. conduct software design walkthrough

H) Creating a Structured Program Flowchart

describes software logic (Fig. 2.12)

I) What are Process Specification Tools?

describe elementary level processes

• Structured English (pseudocode) (Fig. 2.14)
• Decision tables (Fig. 2.15)
• Decision trees (Fig. 2.16)
• Equations

J) Creating a Warnier-Orr Diagram

uses brackets to show hierarchical decomposition of processes or data (Fig. 2.17)

• Prepare a Logical View (use Venn Diagrams)
• Map the solution into a WOD (Fig. 2.19)

K) Creating a Jackson Diagram

uses input and output of the data to create the program structure (Fig. 2.20)

1. Define Input and Output Data Structures (Fig. 2.21)
2. Determine the Program Correspondences between Data Structures
3. Develop the Software Structure (Fig. 2.22)
4. Write Structured Text (Fig. 2.23)

Exercises: look over 1-23, ; turn in 2.24, 2.26, 2.28, 2.30, 2.34, 2.36, 2.42