Systems Analysis & Design
(Sixth Edition)
PHASE 2: SYSTEMS ANALYSIS
Chapter 4
Data and Process Modeling
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Chapter Objectives
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Describe data and process modeling concepts and
tools, including data flow diagrams, a data
dictionary, and process descriptions
Describe the symbols used in data flow diagrams
and explain the rules for their use
Draw data flow diagrams in a sequence, from
general to specific
Explain how to level and balance a set of data flow
diagrams
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Chapter Objectives
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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
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Introduction
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In Chapter 4, we will use data and process modeling
techniques …
To develop a logical model of the proposed system
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Logical model  WHAT system must do
Physical model  HOW system will be constructed (later
in systems design phase)
To document system requirements
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Overview
Data and Process Modeling Tools
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Systems analysts use many graphical
techniques to describe an information system
A data flow diagram (DFD) uses various
symbols to show how the system transforms
input data into useful information
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Data Flow Diagrams
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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
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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
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Data Flow Diagrams
DFD Symbols
PROCESS symbol
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Receives input data and produces output that has a
different content, form, or both
Contains the business logic  business rules
Referred to as a black box
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Data Flow Diagrams
DFD Symbols
DATA FLOW symbol
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Represents one or more data items
The symbol is a line with a single or double arrowhead
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Fork  same data
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Data Flow Diagrams
DFD Symbols
Basic rules for all PROCESSES and DATA FLOWS
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At least 1 data flow must enter and 1 data flow must exit each
process
AVOID:
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Spontaneous generation
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Black hole
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Has no input
Produces no output
Gray hole
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Input insufficient to generate output
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Data Flow Diagrams
DFD Symbols
DATA STORE symbol
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Represent data that the system stores
Physical characteristics of data store are unimportant
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Concerned only with logical model
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Data Flow Diagrams
DFD Symbols
Basic rules for all DATA STORES
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Data cannot be moved from one store to another
Data cannot move from an outside source to a data store
Data cannot move directly from a data store to a data sink
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Data Flow Diagrams
DFD Symbols
ENTITY Symbol
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Symbol is a rectangle
Depicts origin and/or destination of data
Sometimes referred to as external entity
Name of the entity appears inside the symbol
AKA:
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Terminators  final destination
Source  supplies data
Sink  receives data
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Data Flow Diagrams
DFD Symbols
Basic rules for all ENTITIES (i.e. sources/sinks)
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Entity must be connected to a process by a data flow and
not directly to a data store
Data cannot move directly from a source to a sink
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Data Flow Diagrams
Basic rules for connecting processes, data stores, and
entities in a DFD
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Creating a Set of DFDs
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Create a graphical model of the information
system based on your fact-finding results
Performing three main tasks
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Step 1: Draw a context diagram
Step 2: Draw a diagram 0 DFD
Step 3: Draw the lower-level diagrams
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Creating a Set of DFDs
1. Draw a Context Diagram
Process 0
represents
system
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Creating a Set of DFDs
Draw a Context Diagram
Context Drawing Guidelines
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(Page 156, Figure 4-13)
Fit on one page
Name of information system  Process name
Use unique names within each set of symbols
Do not cross lines
Obtain user input and feedback
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Creating a Set of DFDs
Context Diagram
Refer to Figure 4-13 on page 156 of textbook
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What is the name of the system in this Context Diagram?
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How many sources of data are there? What are they?
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Which entities (sinks) do not supply inputs to the Order
System?
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What data is going into the Order System from Customer?
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What data is going to the Warehouse from the Order
System?
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Creating a Set of DFDs
Draw a Level-0 DFD Diagram
2. Draw a Level-0 Diagram
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Creating a Set of DFDs
Draw a Level-0 DFD Diagram
Level-0 DFD Drawing Guidelines (p. 161, Figure 4-16)
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Decomposition of Context diagram
Parent/Child diagram
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KEEP all data flows into and out of process 0
KEEP all entities
Functional primitive
Diverging data flow – different locations
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Creating a Set of DFDs
Draw Lower Level 1-n DFD Diagrams
Level 1-N Diagrams
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Creating a Set of DFDs
Draw Lower Level 1-n DFD Diagrams
Level 1-n DFD Drawing Guidelines
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Leveling
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Balancing
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Creating a Set of DFDs
Draw a Level-0 DFD Diagram
2. Draw a Level-0 Diagram
Ci1
Wo
Co
C2
Wi
Ci2
So
Bo
Ao
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Creating a Set of DFDs
Draw Lower Level 1-n DFD Diagrams
Level 1-N Diagrams
Co
Ci1
Wo
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Data Dictionary
Central Storehouse (aka Data Repository)
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Facts about system
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Data elements (aka Field)
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Record (aka Data Structures)
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Data Dictionary
Documenting the Data Elements
Objective:
Provide clear,
comprehensive information
about the data and
processes that make up
the system
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Data Dictionary
Documenting the Data Elements
The following attributes are recorded and described:
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Data element name or label
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Alias
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Type and length
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Default value
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Acceptable values - Domain and validity rules
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Data Dictionary
Documenting the Data Elements
The following attributes are recorded and described:
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Source
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Security
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Responsible user(s)
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Description and comments
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Data Dictionary
Documenting the Data Flows
Typical attributes of data flows:
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Data flow name or label
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Description
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Alternate name(s)
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Origin
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Destination
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Record
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Volume and frequency
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Data Dictionary
Documenting the Data Stores
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Typical attributes of a data
store:
Data store name or label
Description
Alternate name(s)
Attributes
Volume and frequency
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Data Dictionary
Documenting the Processes
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Typical attributes of a
process:
Process name or label
Description
Process number
Process description
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Data Dictionary
Documenting the Entities
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Typical attributes of an
entity:
Entity name
Description
Alternate name(s)
Input data flows
Output data flows
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Data Dictionary
Documenting the Records
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Typical attributes of a
record:
Record or data
structure name
Definition or description
Alternate name(s)
Attributes
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Data Dictionary
Data Dictionary Reports
Many valuable reports may be obtained
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Data Element report
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Data Flows/Stores report
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Detailed reports
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Process Description Tools
A process description documents the details of a
functional primitive
AND represents a specific set of processing
steps and business logic
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Process Description Tools
Modular Design
Based on the combination of 3 logical structures
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Sequence
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Selection
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Iteration - looping
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Process Description Tools
Typical process tools include:
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Structured English
Decision Tables
Decision Trees
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Process Description Tools
Structured English
Purpose: Describe underlying business logic
Structured English Rules
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Use 3 building blocks
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Sequence, Selection, Iteration
Use indentation for readability
Use limited vocabulary
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Standard terms used in data dictionary
Specific words that describe the processing rules
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Process Description Tools
Structured English (Pg. 174, Figure 4-37)
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Might look familiar because it resembles
pseudocode
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Process Description Tools
Decision Tables
Decision Tables
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Logical structure  All combinations of conditions
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Resulting actions
VERIFY ORDER Process
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1
3
1.
2.
3.
Conditions
Combo of Y/N for condition – 4 diff. rules or combos
X to accept or reject order given the rule
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Process Description Tools
Decision Tables
Decision Tables
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Can have > 3 possible outcomes
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Best way to describe complex set of conditions
Sales Promotion Policy
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Process Description Tools
Decision Trees
Decision Trees
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Graph of conditions, actions, rules in decision table
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Personal preference  Decision table or tree
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Logical Versus Physical Models
Four-Model Approach
What analysts can do …
1st Create a physical model of current system
2nd Develop a logical model of current system
3rd Develop a logical model of new system
4th Develop a physical model of new system
Disadvantage: Added time and cost
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Chapter Summary
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During data and process modeling, a systems analyst develops
graphical models to show how the system transforms data into
useful information
The end product of data and process modeling is a logical
model that will support business operations and meet user
needs
Data and process modeling involves three main tools: data flow
diagrams, a data dictionary, and process descriptions
Data flow diagrams (DFDs) graphically show the movement
and transformation of data in the information system
DFDs use four symbols
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Chapter Summary
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A set of DFDs is like a pyramid with the context diagram at
the top
The data dictionary is the central documentation tool for
structured analysis
Each functional primitive process is documented using
structured English, decision tables, and decision trees
Structured analysis tools can be used to develop a logical
model during one systems analysis phase, and a physical
model during the systems design phase
Any questions?
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