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

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 Systems Analysis and Design for the Small Enterprise Chapter 3 2

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 Systems Analysis and Design for the Small Enterprise Chapter 3 3

Figure 3-1: DFD and the Six CIS Components Systems Analysis and Design for the Small Enterprise Chapter 3 4

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. Systems Analysis and Design for the Small Enterprise Chapter 3 5

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 Systems Analysis and Design for the Small Enterprise Chapter 3 6

Figure 3-3: Illustrated DFD Symbols Systems Analysis and Design for the Small Enterprise Chapter 3 7

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 Systems Analysis and Design for the Small Enterprise Chapter 3 8

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 Systems Analysis and Design for the Small Enterprise Chapter 3 9

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. Systems Analysis and Design for the Small Enterprise Chapter 3 10

Figure 3-5: Silhouette’s Bottom-Up DFD Worksheet Action words identified in the narrative Systems Analysis and Design for the Small Enterprise Chapter 3 11

Figure 3-6: Silhouette’s Task #1 Evaluate Special Requests IPO Chart Systems Analysis and Design for the Small Enterprise Chapter 3 12

Figure 3-7: Silhouette Sea Charter’s Partial DFD Sketch Systems Analysis and Design for the Small Enterprise Chapter 3 13

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 Systems Analysis and Design for the Small Enterprise Chapter 3 14

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 Systems Analysis and Design for the Small Enterprise Chapter 3 15

Figure 3-9: TKSystem Context Diagram Systems Analysis and Design for the Small Enterprise Chapter 3 16

Figure 3-10: Revised TKSystem Context Diagram Systems Analysis and Design for the Small Enterprise Chapter 3 17

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 Systems Analysis and Design for the Small Enterprise Chapter 3 18

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 Systems Analysis and Design for the Small Enterprise Chapter 3 19

Figure 3-12: TKSystem Issue Access Cards Task DFD Systems Analysis and Design for the Small Enterprise Chapter 3 20

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 Systems Analysis and Design for the Small Enterprise Chapter 3 21

Figure 3-13: TKSystem First-Level DFD Enlarge Enlarge Systems Analysis and Design for the Small Enterprise Chapter 3 22

Figure 3-14: Data Flow Walk-Through Systems Analysis and Design for the Small Enterprise Chapter 3 23

Figure 3-15: TKSystem DFD Levels Systems Analysis and Design for the Small Enterprise Chapter 3 24

Thinking Critically Model Building for Pay How would you respond to a client who asks why he or she should pay for model building? Systems Analysis and Design for the Small Enterprise Chapter 3 25

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. Systems Analysis and Design for the Small Enterprise Chapter 3 26

Figure 3-16: Cornucopia Existing System Context Diagram Systems Analysis and Design for the Small Enterprise Chapter 3 27

Figure 3-17: Cornucopia Existing System First-Level DFD Detail Detail Detail Detail Systems Analysis and Design for the Small Enterprise Chapter 3 28

Figure 3-18: Cornucopia Process Modeling with Visible Analyst Enlarge Systems Analysis and Design for the Small Enterprise Chapter 3 29

Figure 3-19: Cornucopia Existing System Context Diagram in Visible Analyst Enlarge Systems Analysis and Design for the Small Enterprise Chapter 3 30

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 Systems Analysis and Design for the Small Enterprise Chapter 3 31

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 Systems Analysis and Design for the Small Enterprise Chapter 3 32

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 Systems Analysis and Design for the Small Enterprise Chapter 3 33

Figure 3-13: TKSystem First-Level DFD (top) Return Systems Analysis and Design for the Small Enterprise Chapter 3 34

Figure 3-13: TKSystem First-Level DFD (bottom) Return Systems Analysis and Design for the Small Enterprise Chapter 3 35

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) Return Systems Analysis and Design for the Small Enterprise Chapter 3 36

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) Return Systems Analysis and Design for the Small Enterprise Chapter 3 37

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) Return Systems Analysis and Design for the Small Enterprise Chapter 3 38

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) Return Systems Analysis and Design for the Small Enterprise Chapter 3 39

Systems Analysis and Design For the Small Enterprise Figure 3-18 Enlargement Return Systems Analysis and Design For the Small Enterprise Chapter 2 40

Systems Analysis and Design For the Small Enterprise Figure 3-19 Enlargement Return Systems Analysis and Design For the Small Enterprise Chapter 2 41