1. Modeling the Processes and Logic
Chapter 5
Modeling the Processes and Logic

2. Learning Objectives
Understand the basic concepts of logical process modeling
Draw DFDs using specific rules and components to depict logical process models
Understand the hierarchy of DFDs using the concept of functional decomposition
SAD/CHAPTER 5

3. Learning Objectives
Understand the differences between DFDs and flowcharts.
Understand the four basic logic modeling techniques of structured English, decision tables, decision trees, and state-transition diagrams and be able to select the appropriate tool for the conditions
SAD/CHAPTER 5 5-

4. Logical Process Modeling
The “What” versus the “How”
Logical Model versus Physical Model
Physical model: what the system and exactly how it does it
Logical Model: What a system is or does without any of the constraints of how that might be accomplished
SAD/CHAPTER 5

5. Benefits of Logical Model
Reduces the risk of overlooking important business requirement due to the analyst becoming preoccupied with the technical elements
Reduces the biases associated with the way the current system is implemented
Analysts can communicate with users easily
SAD/CHAPTER 5

6. Data Flow Diagram
A graphical tool that depicts the sequence of processes and functions contained within a specific system boundary and the flow of data through that system
SAD/CHAPTER 5

7. DFD Symbols Four basic symbols Two popular symbol sets Process
Data Flow
Data Store
External Entity
Two popular symbol sets
Gane and Sarson
DeMarco and Yourson
SAD/CHAPTER 5

8. Figure 5-1. Comparison of DFD Symbols
SAD/CHAPTER 5

9. DFD Components Data Flow
Represented by a line with arrowhead indicating direction of flow
Data in motion
Use noun to name the data content
SAD/CHAPTER 5

10. DFD Components Data Store
Represents a repository for data recorded within the system
Data at rest
SAD/CHAPTER 5

11. DFD Components Process Transform data into another form
Process inputs to create a set of output data flows
Using the input as output in its same basic form
Reorganize the inputs
SAD/CHAPTER 5

12. DFD Components External agent
Someone or something interacts with the system but resides outside the system boundary
Source: serve as the origin of data flowing into the system
Sink: represents a destination for data flowing out from the system
SAD/CHAPTER 5

13. Figure 5-2. Data Flow Diagram for Logical Apple-Peeling Process
SAD/CHAPTER 5

14. DFD Hierarchy System is composed of a decomposable set of subsystems
By creating a top-down decomposed hierarchy of diagrams, each with a greater degree of detail than the last, we can understand the complexity of the system
SAD/CHAPTER 5 5-

15. Figure 5-3. Numbering Convention for DFD Decomposition
SAD/CHAPTER 5

16. Context Level Diagram Shows the system boundary
Contain only one process, labeled with the name of the system, assigned a zero as its identifier
Data flow connects the process to its source and sink entities
SAD/CHAPTER 5

17. Figure 5-4. Context-Level Diagram for Employee Payroll System
SAD/CHAPTER 5

18. Level-0 DFD More detail than the context diagram
Major processes within the system
Sequence of those processes
Data stores accessed by those processes
Source and sink entities that interact with the system
SAD/CHAPTER 5

19. Figure 5-5. Level-0 Data Flow Diagram for Employee Payroll System
SAD/CHAPTER 5

20. Level-1 through Level-n DFD
Level-0 is decomposed to a required level of detail for all processes
All data flows entering or leaving a parent process must also be shown as entering or leaving the set of child processes
No more than seven levels should be developed
When a process has been fully decomposed to the desired level of detail, it is referred to as a functional primitive
SAD/CHAPTER 5

21. Figure 5-6. Level-1 Data Flow Diagram for Employee Payroll System
SAD/CHAPTER 5

22. Figure 5-7. Excerpt from Fully Decomposed DFD fro Employee Payroll System
SAD/CHAPTER 5

23. DFDs versus Flowcharts
a diagram that specifies all programs, inputs, outputs, and data store accesses and retrievals
depicts the specific flow of control through an IS
SAD/CHAPTER 5

24. Figure 5-8. ANSI System Flowchart Symbology
SAD/CHAPTER 5

25. Figure 5-9. System Flowchart Example
SAD/CHAPTER 5

26. DFD Guidelines Establish system boundary.
Label processes and data flows with sufficient information.
Think WHAT and not HOW.
Think data FLOW, not control.
SAD/CHAPTER 5

27. Analyzing and Using the DFD
Constant verification is the key to an accurate set of DFDs.
DFD should be carefully reviewed with end users.
DFD should be checked against the stated system objectives.
SAD/CHAPTER 5

28. Modeling Process Logic
A technique used to model the sequential or temporal logic contained within the processes
Structured English
Decision tables
Decision Trees
State-Transition Diagram
SAD/CHAPTER 5

29. Structured English Use three logic constructs
Repetition
Decision
Sequential
Each process must have only one entrance and only one exit
SAD/CHAPTER 5

30. Table 5-2. Structured English representation of Common Procedural Structures
SAD/CHAPTER 5

31. Table 5-2. Structure English representation of common Procedural Structures
SAD/CHAPTER 5

32. Table 5-3. Structure English Examples for process 4.0
SAD/CHAPTER 5

33. Figure 5-10. Functional-Primitive Decomposition for the Process 4.0
SAD/CHAPTER 5

34. Decision Tables
A diagram of all the logic and possible outcomes associated with a particular process
Process rules
Condition stubs
Action stubs
SAD/CHAPTER 5

35. Decision Tables Process rule and condition stubs Action stubs
represent the specific rule when making a decision
Action stubs
represent all possible courses of action associated with a given set of conditions and rules
SAD/CHAPTER 5

36. Table 5-4. Structured English logic for Insurance Rating System
SAD/CHAPTER 5

37. Table 5-5. Decision Table for Insurance Rating System
SAD/CHAPTER 5

38. Table 5-6. Procedure for Constructing Decision Tables
SAD/CHAPTER 5

39. Decision Trees
Graphical representation of logic in a “tree trunk and branches” shape
Decision Points (nodes)
the sequence in which the decision are made
Actions
description of action to be taken are connected to a node by an arrow
SAD/CHAPTER 5

40. Figure 5-11. The basic Structure of a NonProbabilistic Decision Tree
SAD/CHAPTER 5

41. Figure 5-12. Decision Tree for Insurance Rating System
SAD/CHAPTER 5

42. State Transition Diagram
Models how two or more processes are related to each other in time
Illustrates the various states a system component can take in relation to the events or conditions that cause a change from one state to another
SAD/CHAPTER 5

43. State Transition Diagram
State: a condition of existence that can be taken by a system component
When an event occurs, a transition triggered, and the system component assumes a different state, thus causing an action to occur
SAD/CHAPTER 5

44. Figure 5-13. State-Transition Diagram for generic Three-State Event
SAD/CHAPTER 5

45. State Transition Diagram
State Transition Diagram steps
Identify the initial state.
Represent that state by drawing a rectangle on the diagram.
Connect that state with an arrow to show its first transition.
Each state should lead to at least one other state.
SAD/CHAPTER 5

46. State Transition Diagram
State Transition Diagram steps (cont.)
Label the arrow with a descriptive event name.
List the appropriate actions to be taken adjacent to each state rectangle.
Consider system actions to unexpected events.
Repeat the process until all possible states are accounted for.
SAD/CHAPTER 5

47. Figure 5-14 (a). State transition Diagram for Elevator Floor Request Logic
SAD/CHAPTER 5

48. Figure 5-14 (b). State transition Diagram for Door Control Request Logic
SAD/CHAPTER 5

49. Criteria for Determining Appropriate Logic Modeling Technique
Table Criteria For Determining Appropriate Logic Modeling Technique
SAD/CHAPTER 5 - End -

50. Chapter Summary
By reducing a complex system into a set of logical models, the analyst can easily view the system in a holistic sense.
Using the various modeling tools, the analyst must be able to analyze complex logic sequences and organize them into a set of instructions.
SAD/CHAPTER 5

51. Chapter 5
End of Chapter