1. Phase 2 – Systems Analysis
Data and Process Modeling
Chapter 4
Second of four chapters in Systems Analysis Phase. It explains how to represent system data and processes graphically.

2. Objectives Describe data and process modeling concepts and tools
Explain how structured analysis describes an information system.
Describe the symbols used in data flow diagrams.
Explain the sequence of data flow diagrams, from general to specific.
Explain how to level and balance a set of data flow diagrams.
Draw a complete set of data flow diagrams for an information system.

3. Objectives
Describe how a data dictionary is used and what it contains.
Use process description tools, including structured English, decision tables, and decision trees.
Explain the interaction among data flow diagrams, the data dictionary, and process description.
Describe the relationship between logical and physical models.

4. STRUCTURED ANALYSIS
Describes a system in terms of its inputs, outputs , data and processes
Analysts use data and process modeling to show how system processes transform data into useful information
End product is a logical model
Shows what a system must do, regardless of how it will be accomplished physically

5. STRUCTURED ANALYSIS IS is large and complex
Structured analysis provides methods for analyzing, organizing, controlling and documenting large, complex systems

6. STRUCTURED ANALYSIS Is appropriate for business information systems
Data driven systems
data initiates procedures that transform data from one form into information

7. STRUCTURED ANALYSIS Document IS data and data transformations
DATA FLOW DIAGRAMS
DATA DICTIONARY
PROCESS DESCRIPTIONS

8. DATA FLOW DIAGRAMS
Shows how data moves and changes through IS in graphical top-down fashion
essential model
not used to show program logic or detailed logic

9. 4-1

11. Process Symbol
A PROCESS modifies, or changes, data from one form to another from.
data is input to a process, the process transforms data to produce output data of a different content or form

12. PROCESS Symbol Place name of process inside the symbol
Name the process to identify the function it accomplishes
Name consists of active verb, followed by singular noun

13. PROCESS SYMBOL EXAMPLES PREPARE CHECKS POST CUSTOMER PAYMENTS
CALCULATE TAXES
DETERMINE PAST DUE ACCOUNTS
DETERMINE DEAN’S LIST STUDENTS

14. PROCESS NAMES APPLY PAYMENT CALCULATE PAYMENT ASSIGN FINAL GRADE
VERIFY ORDER
FILL ORDER

15. PROCESS Details of process are not shown in DFD
Details of process are documented in process description
BLACK BOX in DFD
We know general inputs, outputs and functions, but not underlying details

16. Black Box approach
allows us to represent processing flow of IS in a series of increasingly detailed diagrams without cluttering more general diagrams with unnecessary details

17. Data Flow Symbol
pathway by which data moves from one part of the information system to another part
represents a specific piece of data or set of data
single data item – ex. name
set of data -- class roster or processed order

18. Data Flow Symbol Details are not shown in DFD
Details are defined in data dictionary

19. Data Flow Symbol
Symbol for data flow is a line segment with single arrowhead
Line segment can be straight or curved
arrowhead indicates direction the data flows

20. Data Flow Symbol Name the dataflow to identify the data it represents
Name consists of adjectives (if necessary) and singular noun

21. Data Flow Symbol Examples BANK DEPOSIT INVOICE PAYMENT STUDENT GRADE
ORDER
GRADING PARAMETERS ???

22. Combining Process and Data Flow symbols
Process must act on an input, and produce output
Process must have at least 1 input data flow and at least 1 output data flow

23. 4-3

24. Combining Process and Data Flow symbols
Illegal representations …
Spontaneous Generation --Process that has no input
Black hole Process that has no output
Gray hole has a least 1 input and 1 output, input is insufficient to generate output shown

25. 4-4

26. Data Store Symbol data repository
when system must store data because one or more processes need to use the stored data at a later time
time length of storage is unimportant

27. Data Store Symbol
Symbol is a flat rectangle that is open on the right side and closed on the left side

28. Data Store Symbol Place name of data store between lines
Name data store to identify category of data it contains
Name consists of plural noun and any supporting adjectives

29. Data Store Symbol Examples STUDENTS ACCOUNTS RECEIVABLE
PURCHASE ORDERS
EMPLOYEES

30. Data Store Symbol Must be connected to a process with a data flow
Must have at least 1 incoming data flow
Must have at least 1 outgoing data flow
Both incoming and outgoing data flows must connect to a process

31. 4-5

32. SOME DFD RULES
Process must have at least one incoming and one outgoing data flow
Data flow must have one and only one arrow head

33. SOME DFD RULES
Data store must be connected to a data flow with a process at the other end of data flow
Data store must have at least one incoming and one outgoing data flow, with a process on the other end

34. 4-6

35. EXTERNAL ENTITY
Person, department, outside organization, or other IS that provides data to the system or receives data or information from the system

36. EXTERNAL ENTITY Show boundaries of the IS
Interaction with the outside world
Terminators
Source or Origin
Destination or Sink

37. EXTERNAL ENTITY Symbol is rectangle – usually shaded
Place name inside the rectangle
Name is singular form of name of department, outside organization, other IS. or person (position, not name)

38. EXTERNAL ENTITY Examples CUSTOMER STUDENT EMPLOYEE ACCOUNTING
PAYROLL SYSTEM
INTERNAL REVENUE SERVICE

39. EXTERNAL ENTITY
SOURCE
DESTINATION
BOTH

40. 4-7

41. Rules for External Entities
Always connected by a data flow to a process
External Entities are never connected to each other

42. 4-8

44. CONTEXT DIAGRAM Top-level view of IS Shows boundaries and scope of IS
Place one process symbol in center of page
Draw external entities around perimeter of page
Connect external entities to process with data flows
Do not show data stores – internal to IS

45. Context Diagram Determine External Entities and Data Flows
Review IS requirements
Identify External Entities
Identify Name and content of data flows
Identify direction of data flow

46. Conventions for DFD’s One Page
Process name for context diagram is name of system
Process name for lower level diagrams is active verb
Unique names for each set of symbols

47. Conventions for DFD’s Avoid crossing lines
Max of process symbols in one diagram
May duplicate external entity or data store
Document any duplication
Use abbreviated identifications for Data Dictionary (process, data store, external entity)

48. Context Diagram General view of IS
Entire IS represented by single process symbol

49. Diagram 0 Data flow diagram that gives more detailed view of IS
show major processes, data flows, and data stores for IS
All external entities from Context Diagram are on Diagram 0

50. Diagram 0 Diagram 0 is more detailed version of process 0
Diagram 0 is EXPLODED version of process 0
Partitioned
Decomposed

51. LEVELING DFD’s
DFD technique of representing graphical model of IS first as a single process, then in greater and greater detail, until only processes are functional primitives

52. Functional Primitive
Process that consists of a single function that is not exploded further

53. LEVELING EXPLODING , PARTITIONING, DECOMPOSING the processes in DFD’s
DFD’s are top-down, general to detail
Each level shows increased detail

54. Leveling considerations
Diagram 0 represents highest level view of IS
Larger more complex systems need more levels
Not all processes need to be exploded same number of levels

55. Required symbols on lower level DFD’s
BALANCED DFD’s -- parent process’s input and output data flows are preserved on child data flow diagram
Data stores on highest level DFD that has 2 or more processes that use that data store

62. DFD rules and lower level diagrams
Notice that Customers data store has outgoing data flow in diagram 1, but no incoming data flow
Is this OK???

63. DATA DICTIONARY
Central storehouse of data about IS data and data transformations
Use data dictionary throughout SDLC and system operation
Use data dictionary even if you don’t use DFD’s

64. Data Dictionary
Document the contents of data flows, data stores, external entities and processes in DFD’s
Data elements (smallest piece of data with meaning in IS) -- data item or field

65. Data elements in Data Dictionary
Must document every data element
Alternate name -- synonym or alias
Output format -- edit mask
Prompt or column header -- field caption
Acceptable values -- domain

66. 4-24

67. 4-25

69. Data Flows in Data Dictionary
Must document every data flow
Abbreviation not identified on DFD
Record
Origin / Destination
Volume and frequency

71. Data stores in Data Dictionary
Must document every data store
Data store name
Abbreviation - matches DFD
Record
Input / Output data flows
Volume and frequency

73. Processes in Data Dictionary
Must document every process that is a FUNCTIONAL PRIMITIVE
Process name
Purpose
Input / Output data flows
Details later

75. External Entities in Data Dictionary

76. Records in Data Dictionary
Data Elements logically combined to form records
Must document all records in Data Dictionary
Data element content - list all elements included in record

77. Records in Data Dictionary
data element names must match data elements in data dictionary
Primary key - uniquely identifies a record PK

78. PROCESS DESCRIPTION TOOLS
Documents details of a functional primitive
details documented in precise, concise manner
One process description for each functional primitive

79. PROCESS DESCRIPTION
SEQUENCE
SELECTION
ITERATION

81. STRUCTURED ENGLISH Uses sequence, selection and iteration
Use indentation for readability
Use limited vocabulary to describe processing rules (IF, FOR EACH, OUTPUT)

82. STRUCTURED ENGLISH similar to pseudocode
Process descriptions should be understandable to end users and system designers
Captialized words are in data dictionary

84. DECISION TABLES tabular description of a selection structure
often better tool than structured English for describing selection process -- especially complex structures

85. DECISION TABLE

86. DECISION TABLES
Because each condition is either true or false, the number of rules doubles each time you add a condition
Easy to construct and verify

87. DECISION TREES Graphical representation of a selection structure
Form of a tree with the roots at the left and branches to the right
Presents same situation as decision table

88. DECISION TREE Decision table and Decision Tree are equivalent
Different form -- graph vs. table
Tree has same number of end branches as the table has columns

90. Automated Structured Analysis
CASE tools reduce amount of clerical work required to organize and document IS
minimize chance for error

91. Logical versus Physical Model
Logical model created during systems analysis phase
Logical model used as basis for physical model
Physical model created during systems design phase
Logical model describes what must happen
Physical model describes how it is to be implemented

92. Softwear, Limited
Rick, SA and Carla, PA, continue their work on the payroll project.
Completed detailed interviews
Understand how current system operates
New requirements desired by users
Ready to organize findings and documents with a logical model.
Context Diagram

93. 4-42

94. 4-43

95. 4-44

96. 4-45

97. 4-46

99. New Century Health Clinic Case Study
Prepare context diagram for New Century’s information system
Prepare diagram 0 for New Century
4 processes documented
Include at least 1 data store
Follow our DFD rules/conventions