1. section II Analysis Systems Analysis and Design
chapter3
section II
Analysis
for the Small Enterprise
Systems Analysis and Design
modeling the system
the data flow diagram
the context diagram
level decomposition
the cornucopia case
portfolio project

2. When you complete this chapter you will be able to:
Chapter Objectives
When you complete this chapter you will be able to:
Describe why the data flow diagram is called a process model
Recognize and describe an abstraction
Identify the four elements of a data flow diagram
Construct a data flow diagram
Decompose a data flow diagram
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3. Process model: diagrams how data flows through the system
Modeling the System
Process model: diagrams how data flows through the system
Data model: diagrams the relationships between data files
Object model: diagrams the relationships between enterprise objects
System models: diagram system functions, hardware, and software
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4. Figure 3-1: DFD and the Six CIS Components
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5. Abstractions and Computer Information Systems
TECHNOTE 3-1
Abstractions and Computer Information Systems
An abstraction is a simplified description, view, or model of an object or system of objects.
The process, data, object, and system models are abstractions of a computer information system.
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6. The DFD is composed of four elements:
The Data Flow Diagram
The data flow diagram (DFD) presents a picture of what people and procedures do to transform data into information
The DFD is composed of four elements:
External entity … the originator of data (source) or receiver of information (sink)
Process …a series of steps that manipulate data
Data store … a place to keep data for later reference
Data flow … describe data and information elements passing between external entities, processes, and data stores
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7. Figure 3-3: Illustrated DFD Symbols
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8. Standard rules for construction:
The Data Flow Diagram
Standard rules for construction:
Data flows must originate or terminate at a process
Data stores must have at least one entry and one exit data flow
Processes must have at least one entry and one exit data flow
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9. Reference Figure 3-4: Bottom-Up DFD Creation
Data Flow Diagrams
Bottom-Up DFD creation
Develop a narrative of the system
Underline the action words
Develop a sequential list of the action words
Eliminate tasks that do not transform data
Identify cohesive tasks
Fit all remaining tasks to a cohesive task
Develop an IPO chart for each cohesive task
Reference Figure 3-4: Bottom-Up DFD Creation
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10. A portion of Silhouette Sea Charter’s narrative:
Data Flow Diagrams
A portion of Silhouette Sea Charter’s narrative:
Sometimes the office manager cannot determine whether the request is reasonable. When this happens, the request is forwarded to the owner, who makes this determination, contacts the customer if necessary, and either adjusts the request or rejects it outright. All requests are returned to the office manager for scheduling and filing.
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11. Figure 3-5: Silhouette’s Bottom-Up DFD Worksheet
Action words identified
in the narrative
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12. Figure 3-6: Silhouette’s Task #1 Evaluate Special Requests IPO Chart
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13. Figure 3-7: Silhouette Sea Charter’s Partial DFD Sketch
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14. Reference Figure 3-8: Top-Down DFD Creation
Data Flow Diagrams
Top-Down DFD creation
Solicit oral answers to the question “What is the first task of this system?”
Continue with “What happens next?”
Repeat Step 2 until the response is “We do it all over again,” or We are finished.”
Reference Figure 3-8: Top-Down DFD Creation
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15. Connected to the external entities Establishes the system boundaries
The Context Diagram
The context diagram
Shows a single process
Connected to the external entities
Establishes the system boundaries
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16. Figure 3-9: TKSystem Context Diagram
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17. Figure 3-10: Revised TKSystem Context Diagram
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18. Task definition begins by locating the events within a process
Level Decomposition
The single process in the context diagram is composed of a collection of well-defined activities called cohesive tasks
Task definition begins by locating the events within a process
Events identify the end of one task and the beginning of another
Once a task is identified, the analyst can identify the inputs and outputs
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19. Reference Figure 3-11: TKSystem Task IPO
Level Decomposition
Issue Access Cards INPUTS:
class rosters (Source: Data Processing)
access cards for registered students (Source: Data Processing)
student registration (Source: Data Processing)
signed non-piracy agreement (Source: Student)
name on class rosters (Data Store: Roster)
Issue Access Cards OUTPUTS:
access cards (Sink: Student)
lab handbook (Sink: Student)
card numbers already issued (Sink: Data Processing)
checkoff on class rosters (Data Store: Roster)
new lab account (Data Store: Time)
nonpiracy agreement (Data Store: Agreements)
Reference Figure 3-11: TKSystem Task IPO
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20. Figure 3-12: TKSystem Issue Access Cards Task DFD
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21. Logical and Physical DFDs
TECHNOTE 3-2
Logical and Physical DFDs
Logical DFDs remove all reference to the implementation specifics of the system
Physical DFDs specify the real world objects that are used to make the system work
During the analysis phase:
Develop the physical DFD
Abstract the logical DFD
During the design phase:
Develop the logical DFD
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22. Figure 3-13: TKSystem First-Level DFD
Enlarge
Enlarge
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23. Figure 3-14: Data Flow Walk-Through
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24. Figure 3-15: TKSystem DFD Levels
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25. Thinking
Critically
Model Building for Pay
How would you respond to a client who asks why he or she should pay for model building?
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26. THE CORNUCOPIA CASE The Cornucopia Case
The analysis phase is well underway. The analysts must first understand the existing system before the new system can be designed. The process model is the first abstraction to develop.
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27. Figure 3-16: Cornucopia Existing System Context Diagram
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28. Figure 3-17: Cornucopia Existing System First-Level DFD
Detail
Detail
Detail
Detail
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29. Figure 3-18: Cornucopia Process Modeling with Visible Analyst
Enlarge
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30. Figure 3-19: Cornucopia Existing System Context Diagram in Visible Analyst
Enlarge
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31. Portfolio project Portfolio Project
Team Assignment 3: Process Modeling
Prepare the existing system context diagram and first-level DFD
Review the project management sections of Appendices A and B
Develop the first draft of your week-by-week project budget
Develop the first draft of your week-by-week project status
Prepare a cover letter to transmit the budget and status reports to your client
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32. Chapter Summary (1/2)
The data flow diagram (DFD) models the processes of an information system
DFDs consist of processes, external entities, data stores, and data flows
DFD modeling begins with the context diagram, which depicts the entire system in a single process symbol surrounded by external entities
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33. Chapter Summary (2/2)
The first-level DFD shows the major functional components of the system as processes, connected by data flows to external entities, data stores, and other processes
As needed, successively more detailed levels are developed to promote complete understanding of the system
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34. Figure 3-13: TKSystem First-Level DFD (top)
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35. Figure 3-13: TKSystem First-Level DFD (bottom)
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36. Cornucopia Correspondence Task IPO
Narrative: The owner updates the customer file from personal checks or direct requests from the customers. Mailing labels are printed from this system. The owner creates promotional materials and mails them to customers.
TASK: Customer Correspondence
INPUTS:
personal checks (Source: Customer)
customer requests (Source: Customer)
customer name, address (Data Store: Customer)
OUTPUTS:
mailing labels (Sink: Customer)
promotional material (Sink: Customer)
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37. Cornucopia Inventory Task IPO
Narrative: Employees observe sales activity, noting shortages on a pad next to the cash register. The owner consults a suppler list and places orders, notes the order date on the pad. The employees scratch off these notes as shipments are received.
TASK: Inventory
INPUTS:
observations of inventory (Data Store: Inventory)
observations of sales (Source: Sales System)
OUTPUTS
notes the shortage (Data Store: Orders)
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38. Cornucopia Order Task IPO
Narrative: Employees observe sales activity, noting shortages on a pad next to the cash register. The owner consults a suppler list and places orders, notes the order date on the pad. The employees scratch off these notes as shipments are received.
TASK: Order
INPUTS:
notes the order (Data Store: Order)
consults supplier list (Data Store: Supplier)
supplier changes (Data Store: Supplier)
OUTPUTS
places orders (Sink: Supplier)
notes the date (Data Store: Orders)
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39. Cornucopia Receive Task IPO
Narrative: Employees observe sales activity, noting shortages on a pad next to the cash register. The owner consults a suppler list and places orders, notes the order date on the pad. The employees scratch off these notes as shipments are received.
TASK: Receive
INPUTS:
shipments (Source: Supplier)
OUTPUTS
scratch off order (Data Store: Orders)
shipments (Data Store: Inventory)
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40. Systems Analysis and Design For the Small Enterprise
Figure 3-18 Enlargement
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41. Systems Analysis and Design For the Small Enterprise
Figure 3-19 Enlargement
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