Systems Design

and
Implementation
BIT324
DATA AND PROCESS MODELING
Chapter Objectives 2

• 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
Chapter Objectives 3

 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
Introduction 4

 In the next two, you will 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
Overview of Data and 5

Process Modeling Tools

 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
Data Flow Diagrams 6

 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
Data Flow Diagrams 7

 DFD Symbols
Data Flow Diagrams 8

 DFD Symbols
 Process symbol
 Receives input data and produces output that has a
different content, form, or both
 Contain the business logic, also called business rules
 Referred to as a black box
Data Flow Diagrams 9

 DFD Symbols
 Data flow symbol
 Represents one or
more data items
 The symbol for a
data flow is a line
with a single or
double arrowhead
 Spontaneous
generation
 Black hole
 Gray hole
Data Flow Diagrams 10

 DFD Symbols
 Datastore
symbol
 Represent data
that the system
stores
 The physical
characteristics of
a data store are
unimportant
because you are
concerned only
with a logical
model
Data Flow Diagrams 11

 DFD Symbols
 Entity Symbol
 Name of the
entity
appears
inside the
symbol
Creating a Set of DFDs 12

 Create a graphical model of the information

system based on your fact-finding results
 First, you will review a set of guidelines for drawing
DFDs. Then you will learn how to apply these
guidelines and create a set of DFDs using a three-
step process
Creating a Set of DFDs 13

 Guidelines for Drawing DFDs

 Draw the context diagram so that it fits on one
page
 Use the name of the information system as the
process name in the context diagram
 Use unique names within each set of symbols
Creating a Set of DFDs 14

 Guidelines for Drawing DFDs

 Do not cross lines
 Provide a unique name and reference number for
each process
 Obtain as much user input and feedback as
possible
Creating a Set of DFDs 15

 Step 1: Draw a Context Diagram

Creating a Set of DFDs 16

 Step 2: Draw a Diagram 0 DFD

Creating a Set of DFDs 17

 Step 2: Draw a Diagram 0 DFD

 If same data flows in both directions, you can use a
double-headed arrow
 Diagram 0 is an exploded view of process 0
 Parent diagram
 Child diagram
 Functional primitive
Creating a Set of DFDs 18

 Step 3: Draw the Lower-

Level Diagrams
 Must use leveling and
balancing techniques
 Leveling examples
 Uses a series of
increasingly detailed
DFDs to describe an
information system
 Exploding, partitioning,
or decomposing
Creating a Set of DFDs 19

 Step 3: Draw the Lower-

Level Diagrams
 Balancing Examples
 Ensures that the input
and output data flows
of the parent DFD are
maintained on the
child DFD
Data Dictionary 20

• A data dictionary, or data repository, is a central

storehouse of information about the system’s data
• An analyst uses the data dictionary to collect,
document, and organize specific facts about the
system
• Also defines and describes all data elements and
meaningful combinations of data elements
Data Dictionary 21

 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
Data Dictionary 22

 Using CASE Tools for Documentation

 The more complex the system, the more difficult it is
to maintain full and accurate documentation
 Modern CASE tools simplify the task
 A CASE repository ensures data consistency
 You will learn more about CASE tools in Part 2 of the
Systems Analyst’s Toolkit
 Data Dictionary 23

 Documenting the Data

Elements
 You must document every
data element in the data
dictionary
 The objective is the same: to
provide clear, comprehensive
information about the data
and processes that make up
the system
Data Dictionary 24

 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
Data Dictionary 25

 Documenting the Data Elements

 The following attributes usually are recorded and
described
 Source
 Security
 Responsible user(s)
 Description and comments
Data Dictionary 26

 Documenting the Data Flows

 The typical attributes are as follows
 Data flow name or label
 Description
 Alternate name(s)
 Origin
 Destination
 Record
 Volume and frequency
Data Dictionary 27

 Documenting the Data Stores

 Typical characteristics of a data store are
 Data store name or label
 Description
 Alternate name(s)
 Attributes
 Volume and frequency
Data Dictionary 28

 Documenting the Processes

 Typical characteristics of a process
 Process name or label
 Description
 Process number
 Process description
Data Dictionary 29

 Documenting the Entities

 Typical characteristics of an entity include
 Entity name
 Description
 Alternate name(s)
 Input data flows
 Output data flows
Data Dictionary 30

 Documenting the Records

 Typical characteristics of a record include
 Record or data structure name
 Definition or description
 Alternate name(s)
 Attributes
Data Dictionary 31

• Data Dictionary Reports

– Many valuable reports
• An alphabetized list of all data elements by name
• A report describing each data element and indicating
the user or department that is responsible for data
entry, updating, or deletion
• A report of all data flows and data stores that use a
particular data element
• Detailed reports showing all characteristics of data
elements, records, data flows, processes, or any other
selected item stored in the data dictionary
Process Description Tools 32

• A process description documents the details of a

functional primitive, which represents a specific
set of processing steps and business logic
• It should be noted that this chapter deals with
structured analysis, but the process description
tools also can be used in object-oriented
development, which is described in the next
chapter.
Process Description Tools 33

 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
Process Description Tools 34

 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
Process Description Tools 35

 Structured English
 Might look familiar to programming students
because it resembles pseudocode
 The primary purpose of structured English is to
describe the underlying business logic
Process Description Tools 36

 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
Process Description Tools 37

 Decision Tables
 The number of rules doubles each time you add a
condition
 Can have more than two possible outcomes
 Often are the best way to describe a complex set
of conditions
Process Description Tools 38

 Decision Trees
Logical Versus Physical 39

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
Logical Versus Physical 40

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
Logical Versus Physical 41

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
Chapter Summary 42

• 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
Chapter Summary 43

 Data flow diagrams (DFDs) graphically show the

movement and transformation of data in the
information system
 DFDs use four symbols
 A set of DFDs is like a pyramid with the context
diagram at the top
Chapter Summary 44

• 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
Chapter Summary 45

 Chapter complete