Draw a context diagram and a diagram 0 DFD that represents the information system at a typical library
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Chapter 5
Data and Process Modeling
Learning Objectives (1 of 2)
•After this chapter, you will be able to:
• Describe the relationship between logical and
physical models
• Explain data flow diagrams
• Draw the four basic data flow diagram
symbols
• Explain the six guidelines used when drawing
data flow diagrams
• Draw context diagrams
• Draw diagram 0 data flow diagrams
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Learning Objectives (2 of 2)
• Draw lower-level data flow diagrams
• Explain how to level and balance data flow
diagrams
• Create a data dictionary
• Apply process description tools in modular
design
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Logical Versus Physical Models (1
of 2)
•Logical model
• Shows what the system must do, regardless of
how it will be implemented physically
•Physical model
• Describes how the system will be constructed
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Logical Versus Physical Models (2
of 2)
•Many analysts follow a four-model
approach
• Physical model of the current system
• Logical model of the current system
• Logical model of the new system
• Physical model of the new system
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Data Flow Diagrams
•Systems analysts use graphical
techniques to describe an information
system
• Data flow diagram (DFD)
• Uses various symbols to show how the system
transforms input data into useful information
• Shows how data moves through an information
system but does not show program logic or
processing steps
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Data Flow Diagram Symbols (1 of
9)
•Four basic symbols represent processes,
data flows, data stores, and entities
FIGURE 5-1 Data flow
diagram symbols, symbol
names, and examples of the
Gane and Sarson and
Yourdon symbol sets
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Data Flow Diagram Symbols (2 of
9)
•Process symbols
• Process receives input data and produces
output
• Contains business logic that transforms the
data
• Process name identifies a specific function
• In DFDs, a process symbol can be referred to
as a black box
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Data Flow Diagram Symbols (3 of
9)
•Data flow
symbols
• Line with a single
or double
arrowhead
FIGURE 5-3 Examples of
correct combinations of data
flow and process symbols
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Data Flow Diagram Symbols (4 of
9)
•Data flow and process combinations that
must be avoided
• Spontaneous generation
• Black holes
• Gray holes
FIGURE 5-4 Examples of incorrect combinations of data flow and
process symbols. APPLY INSURANCE PREMIUM has no input
and is called a spontaneous generation process. CALCULATE
GROSS PAY has no outputs and is called a black hole process.
CALCULATE GRADE has an input that is obviously unable to
produce the output. This process is called a gray hole.
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Data Flow Diagram Symbols (5 of
9)
•Data store symbol
• Represent data that the system stores
• DFD does not show the detailed contents of a
data store
• Specific structure and data elements are defined in
the data dictionary
• A data store must be connected to a process
with a data flow
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Data Flow Diagram Symbols (6 of
9)
•Entity symbol
• Shows how the system interfaces with the
outside world
• DFD shows only external entities that provide
data to the system or receive output
• DFD entities also are called terminators because
they are data origins or final destinations
• Source and sink entities
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Data Flow Diagram Symbols (7 of
9)
FIGURE 5-7 Examples of correct uses of external entities in a data flow diagram.
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Data Flow Diagram Symbols (8 of
9)
FIGURE 5-8 Examples of incorrect uses of external entities. An external entity must be connected
by a data flow to a process, and not directly to a data store or to another external entity.
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Data Flow Diagram Symbols (9 of
9)
•Using DFD symbols
FIGURE 5-9 Examples of correct
and incorrect uses of data flows.
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Drawing Data Flow Diagrams (1 of
2)
•Graphical model is created based on factfinding results
• Review guidelines for drawing DFDs
• Apply guidelines and create a set of DFDs
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Drawing Data Flow Diagrams (2 of
2)
•Guidelines
• 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
• Do not cross lines
• Provide a unique name and reference number
for each process
• Ensure that the model is accurate, easy to
understand, and meets the needs of its users
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Drawing a Context Diagram
•First step in constructing a set of DFDs
FIGURE 5-11 Context diagram
DFD for an order system.
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Drawing a Diagram 0 DFD
•Shows the detail inside the black box
FIGURE 5-13 Diagram 0
DFD for the order system.
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Drawing Lower-Level DFDs (1 of
5)
•Leveling and balancing techniques are used
FIGURE 5-14 Diagram 1
DFD shows details of the
FILLORDER process in the
order system
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Drawing Lower-Level DFDs (2 of
5)
FIGURE 5-15 This diagram
does not show the symbols that
connect to data flows entering
or leaving FILL ORDER on the
context diagram.
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Drawing Lower-Level DFDs (3 of
5)
FIGURE 5-16 The order system diagram 0 is
shown at the top of the figure, and exploded
diagram 3 DFD (for the APPLY PAYMENT
process) is shown at the bottom. The two DFDs
are balanced because the child diagram at the
bottom has the same input and output flows as
the parent process 3 shown at the top.
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Drawing Lower-Level DFDs (4 of
5)
FIGURE 5-17 Example of a parent DFD diagram, showing process 0 as a black box.
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Drawing Lower-Level DFDs (5 of
5)
FIGURE 5-18 In the next level of detail, the process 0 black box reveals three processes, two data
stores, and four internal data flows — all of which are shown inside the dashed line.
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Data Dictionary (1 of 11)
•Central storehouse of information about a
system’s data
• An analyst uses the data dictionary to collect,
document, and organize specific facts about a
system
• Defines and describes all data elements and
meaningful combinations of data elements
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Data Dictionary (2 of 11)
•Data element (i.e., data item or field)
• Smallest piece of data that has meaning within
an information system
• Combined into records (i.e., data structures)
• Record: meaningful combination of related data
elements that is included in a data flow or retained
in a data store
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Data Dictionary (3 of 11)
•Using CASE tools for documentation
• More complex the system, more difficult it is to
maintain full and accurate documentation
• Modern CASE tools simplify the task
• A CASE repository ensures data consistency
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Data Dictionary (4 of 11)
•Documenting the data elements
• Every data element in the data dictionary
should be documented
• Objective: provide clear, comprehensive
information about the data and processes that
make up a system
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Data Dictionary (5 of 11)
•Recorded and described attributes
• Data element name and label
• Alias
• Type and length
• Default value
• Acceptable values
• Source
• Security
• Responsible user(s)
• Description and comments
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Data Dictionary (6 of 11)
•Documenting the data flows
• Data flow name or label
• Description
• Alternate name(s)
• Origin
• Destination
• Record
• Volume and frequency
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Data Dictionary (7 of 11)
•Documenting the data stores
• Data store name or label
• Description
• Alternate name(s)
• Attributes
• Volume and frequency
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Data Dictionary (8 of 11)
•Documenting the processes
• Process name or label
• Description
• Process number
• Process description
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Data Dictionary (9 of 11)
•Documenting the entities
• Entity name
• Description
• Alternate name(s)
• Input data flows
• Output data flows
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Data Dictionary (10 of 11)
•Documenting the records
• Record or data structure name
• Definition or description
• Alternate name(s)
• Attributes
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Data Dictionary (11 of 11)
•Data dictionary reports
• Alphabetized list of all data elements
• Report describing each data element and
indicating the user or department
• 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
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Process Description Tools in
Modular Design (1 of 6)
• Documents the details of a functional
primitive and represents a specific set of
processing steps and business logic
• Typical tools: structured English, decision tables,
and decision trees
• Process descriptions in object-oriented
development
• O-O analysis combines data and processes that
act on the data into objects, and similar objects
can be grouped together into classes
• O-O processes are called methods
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Process Description Tools in
Modular Design (2 of 6)
•Modular design
• Based on combinations of logical structures
(i.e., control structures), which serve as
building blocks for the process
• Sequence
• Selection
• Iteration
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Process Description Tools in
Modular Design (3 of 6)
•Structured English
• Subset of standard English that describes
logical processes clearly and accurately
• Use only the three building blocks of sequence,
selection, and iteration
• Use indentation for readability
• Use a limited vocabulary
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Process Description Tools in
Modular Design (4 of 6)
•Decision tables
• Logical structure that shows every
combination of conditions and outcomes
• Number of rules doubles each time a condition
is added
• Best way to describe a complex set of
conditions
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permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Process Description Tools in
Modular Design (5 of 6)
FIGURE 5-35 In this version, dashes have been added to indicate that a condition is not
relevant. At this point, it appears that several rules can be combined.
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Process Description Tools in
Modular Design (6 of 6)
•Decision trees
• Graphical representation of conditions,
actions, and rules found in a decision table
FIGURE 5-36 This example is based on the same
Sales Promotion Policy shown in the decision
tables in Figures 5-34 and 5-35 on the previous
page. Like a decision table, a decision tree shows
all combinations of conditions and outcomes. The
main difference is the graphical format, which many
viewers find easier to interpret
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
Summary
• Structured analysis tools
• Used to develop a logical model during one
systems analysis phase and a physical model
during the systems design phase
• Data and process modeling
• Main tools: DFDs, data dictionary, and process
description
• Each functional primitive process is
documented
• Structured English, decision tables, and decision
trees
Systems Analysis Design, 12th Edition. ©2020 Cengage. May not be copied, scanned, or duplicated, in whole or in part, except for use as
permitted in a license distributed with a certain product or service or otherwise on a password-protected website for classroom use.
