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

2. 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 2

3. 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 3

4. 4 Figure 3-1: DFD and the Six CIS Components

5. Abstractions and Computer Information Systems 5 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. TECHNOTE 3-1

6. 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 6

7. 7 Figure 3-3: Illustrated DFD Symbols

8. 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 8

9. Data Flow Diagrams 9 Bottom-Up DFD creation 1.Develop a narrative of the system 2.Underline the action words 3.Develop a sequential list of the action words 4.Eliminate tasks that do not transform data 5.Identify cohesive tasks 6.Fit all remaining tasks to a cohesive task 7.Develop an IPO chart for each cohesive task Reference Figure 3-4: Bottom-Up DFD Creation

10. 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.

11. Figure 3-5: Silhouette’s Bottom-Up DFD Worksheet 11 Action words identified in the narrative

12. Silhouette’s Task #1 Evaluate Special Requests IPO Chart 12

13. Silhouette Sea Charter’s Partial DFD Sketch 13

14. Data Flow Diagrams 14 Top-Down DFD creation 1.Solicit oral answers to the question “What is the first task of this system?” 2.Continue with “What happens next?” 3.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

15. The Context Diagram 15 The context diagram Shows a single process Connected to the external entities Establishes the system boundaries

16. Figure 3-9: TKSystem Context Diagram 16

17. Figure 3-10: Revised TKSystem Context Diagram 17

18. Level Decomposition 18 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

19. Level Decomposition 19 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

20. Figure 3-12: TKSystem Issue Access Cards Task DFD 20

21. Logical and Physical DFDs 21 TECHNOTE 3-2 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 –Develop the physical DFD

22. Figure 3-13: TKSystem First-Level DFD 22 Enlarge

23. Figure 3-14: Data Flow Walk-Through 23

24. Figure 3-15: TKSystem DFD Levels 24

25. Model Building for Pay 25 ThinkingCritically How would you respond to a client who asks why he or she should pay for model building?

26. 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. 26

27. 27 Cornucopia Existing System Context Diagram

28. 28 Cornucopia Existing System First-Level DFD Detail

29. Chapter Summary (1/2) 29 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

30. Chapter Summary (2/2) 30 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

31. TKSystem First-Level DFD (top) 31 Return

32. TKSystem First-Level DFD (bottom) 32 Return

33. Cornucopia Correspondence Task IPO TASK: Customer Correspondence INPUTS: personal checks (Source: Customer) customer requests (Source: Customer) customer name, address (Data Store: Customer) OUTPUTS: customer name, address (Data Store: Customer) mailing labels (Sink: Customer) promotional material (Sink: Customer) 33 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. Return

34. Cornucopia Inventory Task IPO TASK: Inventory INPUTS: observations of inventory (Data Store: Inventory) observations of sales (Source: Sales System) OUTPUTS notes the shortage (Data Store: Orders) 34 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. Return

35. Cornucopia Order Task IPO 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) supplier changes (Data Store: Supplier) 35 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. Return

36. Cornucopia Receive Task IPO TASK: Receive INPUTS: shipments (Source: Supplier) OUTPUTS scratch off order (Data Store: Orders) shipments (Data Store: Inventory) 36 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. Return