1. Phase 2: Systems Analysis
Chapter 4
Enterprise Modeling

2. Chapter Objectives
Describe enterprise modeling concepts and tools, including entity-relationship diagrams, data flow diagrams, a data dictionary, and process descriptions
Explain how ERDs provide an overview of system interactions
Describe the symbols used in data flow diagrams and explain the rules
Draw data flow diagrams in a sequence, from general to specific 3

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

4. Introduction
In chapter 4, you will use enterprise modeling techniques to develop a logical model of the proposed system and document the system requirements
Logical model shows what the system must do
Physical model describes how the system will be constructed 4

5. Enterprise Modeling Tools
Systems analysts use many graphical techniques to describe an information system
Two popular tools are entity-relationship diagrams and data flow diagrams

6. Entity-Relationship Diagrams
An entity is a person, place, thing, or event for which data is collected and maintained
An initial ERD helps you understand the interaction among system entities and provides an overall view of the system

7. Entity-Relationship Diagrams
Drawing an Initial ERD
The first step is to list the entities that you identified during the fact-finding process and to consider the nature of the relationships that link them
Cardinality
Figure 4-2

8. Entity-Relationship Diagrams
Types of Relationships
1:1, 1:M, M:N

9. Data Flow Diagrams
A data flow diagram (DFD) shows how data moves through an information system but does not show program logic or processing steps
A set of DFDs provides a logical model that shows what the system does, not how it does it

10. Data Flow Diagrams DFD Symbols
DFDs use four basic symbols that represent processes, data flows, data stores, and entities
Gane and Sarson symbol set
Yourdon symbol set
Symbols are referenced by using all capital letters for the symbol name
Figure 4-7

11. Data Flow Diagrams
DFD Symbols
Figure 4-7

12. Data Flow Diagrams DFD Symbols Process symbol and Data flow symbols
Figure 4-8

13. Data Flow Diagrams
Data store symbol

14. Data Flow Diagrams
Entity Symbol

15. Data Flow Diagrams Context Diagrams The first step towards DFDs
Top-level view of an information system that shows the system’s boundaries and scope
Do not show any data stores in a context diagram because data stores are internal to the system
Begin by reviewing the system requirements to identify all external data sources and destinations

16. Data Flow Diagrams
Context Diagrams

17. Data Flow Diagrams Conventions for DFDs
Each context diagram must fit on one page
The process name in the context diagram should be the name of the information system
Use unique names within each set of symbols
Do not cross lines
Use a unique reference number for each process symbol

18. Data Flow Diagrams Diagram 0
Zooms in on the context diagram and shows major processes, data flows, and data stores
Must retain all the connections that flow into and out of process 0
Each process has a reference number
Diverging data flow
Figure 4-19

19. Data Flow Diagrams Diagram 0
If same data flows in both directions, you can use a double-headed arrow
Diagram 0 represents exploded view of process 0
Parent diagram
Child diagram
Functional primitive
Figure 4-20

20. Data Flow Diagrams
Diagram 0 for the Grading System

21. Data Flow Diagrams Lower-Level Diagrams
Created using leveling and balancing techniques
Leveling
Uses a series of increasingly detailed DFDs to describe an information system
Exploding, partitioning, or decomposing
Figure 4-21
Figure 4-22

22. Data Flow Diagrams Lower-Level Diagrams Balancing
Ensures that the input and output data flows of the parent DFD are maintained on the child DFD
Figure 4-23
Figure 4-24
Figure 4-25

23. Data Flow Diagrams Strategies for Developing DFDs
A set of DFDs is a graphical, top-down model
With a bottom-up strategy, you first identify all functional primitives, data stores, entities, and data flows
The main objective is to ensure that your model is accurate and easy to understand

24. Data Flow Diagrams Strategies for Developing DFDs
General rule of thumb is that a diagram should have no more than nine process symbols
To construct a logical model of a complex system, you might use a combination of top-down and bottom-up strategies
The best approach depends on the information system you are modeling
Figure 4-26
Figure 4-27
Figure 4-28

25. Data Dictionary
A data dictionary, or data repository, is a central storehouse of information
An analyst uses the data dictionary to collect, document, and organize specific facts about the system
The data dictionary also defines and describes all data elements and meaningful combinations of data elements

26. Data Dictionary
A data element, also called a data item or field, is the smallest piece of data that has meaning
Data elements are combined into records, also called data structures
A record is a meaningful combination of related data elements that is included in a data flow or retained in a data store
Figure 4-29

27. Data Dictionary Documenting the Data Elements
You must document every data element in the data dictionary
The objective is to provide clear, comprehensive information about the data and processes that make up the system
Figure 4-30
Figure 4-31

28. Data Dictionary Documenting the Data Elements
The following attributes usually are recorded and described
Data element name and label
Alias
Type and length
Default value
Acceptable values - Domain and validity rules

29. Data Dictionary Documenting the Data Elements
The following attributes usually are recorded and described
Source
Security
Responsible user(s)
Description and comments

30. Data Dictionary Documenting the Data Flows
The typical attributes are as follows
Data flow name or label
Description
Alternate name(s)
Origin
Destination
Record
Value and frequency
Figure 4-32

31. Data Dictionary Documenting the Data Stores
Typical characteristics of a data store are
Data store name or label
Description
Alternate name(s)
Attributes
Volume and frequency
Figure 4-33

32. Data Dictionary Documenting the Processes
Typical characteristics of a process
Process name or label
Description
Process number
Process description
Figure 4-34

33. Data Dictionary Documenting the Entities
Typical characteristics of an entity include
Entity name
Description
Alternate name(s)
Input data flows
Output data flows
Figure 4-35

34. Data Dictionary Documenting the Records
Typical characteristics of a record include
Record or data structure name
Definition or description
Alternate name(s)
Attributes
Figure 4-36

35. Data Dictionary Data Dictionary Reports
You can obtain many valuable reports from a data dictionary
An alphabetized list of all data elements by name
A report by user departments of data elements that must be updated by each department
A report of all data flows and data stores that use a particular data element
Detailed reports showing all characteristics

36. Process Description Tools
A process description documents the details of a functional primitive, which represents a specific set of processing steps and business logic

37. Process Description Tools
Modular Design
Based on combinations of three logical structures, sometimes called control structures which serve as building blocks for the process
Sequence
Selection
Iteration - looping
Figure 4-37
Figure 4-38
Figure 4-39

38. Process Description Tools
Structured English
Must conform to the following rules
Use only the three building blocks of sequence, selection, and iteration
Use indentation for readability
Use a limited vocabulary, including standard terms used in the data dictionary and specific words that describe the processing rules

39. Process Description Tools
Structured English
Might look familiar to programming students because it resembles pseudocode
Figure 4-40
Figure 4-41

40. Process Description Tools
Decision Tables
Shows a logical structure, with all possible combinations of conditions and resulting actions
It is important to consider every possible outcome to ensure that you have overlooked nothing
Figure 4-42
Figure 4-43

41. Process Description Tools
Decision Tables
Can have more than two possible outcomes
Often are the best way to describe a complex set of conditions
Figure 4-44

42. Process Description Tools
Decision Trees
Graphical representation of the conditions, actions, and rules found in a decision table
Whether to use a decision table or tree often is a matter of personal preference
Figure 4-45
Figure 4-46

43. Logical Versus Physical Models
While structured analysis tools are used to develop a logical model for a new information system, such tools also can be used to develop physical models of an information system
A physical model shows how the system’s requirements are implemented

44. Logical Versus Physical Models
Sequence of Models
Many systems analysts create a physical model of the current system and then develop a logical model of the current system before tackling a logical model of the new system
Performing that extra step allows them to understand the current system better

45. Logical Versus Physical Models
Four-Model Approach
Develop a physical model of the current system, a logical model of the current system, a logical model of the new system, and a physical model of the new system
The only disadvantage of the four-model approach is the added time and cost