Using data flow diagram

SYSTEM ANALYSIS
AND DESIGN
Chap 7: using Data Flow Diagrams
1AITS-MCA- Kiran Ajudiya

Data Flow Diagrams (DFD)
 Through a structure analysis technique called
data flow diagram.
 Analyzing data-oriented systems
 Inputs
 Processes
 outputs
 Emphasizes system logic
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AITS-MCA- Kiran Ajudiya

Advantages
 Freedom from technical commitment (neutral)
 Clarify systems / subsystems (is this right?)
 Communicates understanding to users (is this
right?)
 Analysis of systems (is anything missing?)
3

Conventions (cont)
 Entity (source / destination: person, dept, machine, business)
 Arrow (data flow: from->to)
 Process (transforming)
 Data store (examination, retrieval, addition)
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Conventions: Basic Symbols
5

DFD Development : Basic
Rules
6
 DFD must have at least one process.
 Process must receive at least one data flow
and at least one leaving from the process.
 Data store should be connected to at least
one process.
 External entities should not connected each
other.

Process Naming:
Inventory Control System Name reflects whole system
Inventory reporting subsystem Name reflects whole subsystem
Verify Customer Account Name reflects specific process
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Creating Context Diagram
9
 Contains only one process (number Zero).
 Representing the entire system (input –
process – output).
 All external entities are shown on the context
diagram.
 Show major data flow.
 Diagram does not contain any data store

Context Diagram
10

Diagram 0 (Next Level)
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 Diagram 0 is the explosion of the context diagram.
 May include up to 9 Process.
 Start with the data flow from an entity on input
side (Forward)
 Work backward from output (Backward)
 Examine Data Flow:
 What processes put data into the store?
 What processes use the data?
 Analyze well define process
 What input & output, appropriate connection or not

Diagram 0 (parent)
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Child Diagram
13
 Each process on diagram 0(zero) may be
exploded to create a child diagram.
 Each process on a lower-level diagram
may be exploded to create another child
diagram.
 Each process is numbered with the parent
diagram number, a period, and a unique
child diagram number.

Child Diagram (Continue….)
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 External entities are usually not shown on
the child diagrams below Diagram 0.
 If the parent process has data flow connecting
to a data store, the child diagram may include
the data store as well.

Child Diagram (Continue…)
15
 A lower-level diagram may contain data
stores not shown on the parent process, such
as:
 A file containing a table of information (such as a
tax table).
 A file linking two processes on the child diagram.
 Minor data flow, such as an error line, may
be included on a child diagram.
 An interface data flow is data that are input or
output from a child diagram that matches the
parent diagram data flow.

Child Diagram (Continue…..)
16
 Processes may or may not be exploded
depending on their level of complexity when a
processes is not exploded it is said to be
functionally primitive and is called a
“PRIMITIVE PROCESS”

Typical Errors in DFD
 Data flow arrow wrong direction / forgetting
 Connecting Data store to entity w/o process
 Incorrect labeling
 Too many processes (>9 on a sheet)
 Omitting data flow
 Creating Unbalanced decomposition in child
diagram.
18

Bad!
19

Good!
20

Logical & physical Data Flow
21
 Logical DFD focused on business and how
business operates.
 It is not worried how the system will be
constructed.
 Physical DFD shows how the system will be
implemented including hardware, software,
files and people involved in the system.

Transition
s22

Logical vs Physical Data Flow
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Developing Logical Flow
Diagrams
 Advantages
 Better communication w/users
 Stable systems
 Understanding of business
 Flexibility and maintenance
 Identify redundancies
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Developing Physical DFD
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 Clarifying which processes are performed by
human and which are automated.
 Describing processes in more detail than logical
DFD
 Sequencing processes that have to be done in a
particular order.
 Identifying temporary data stores.
 Specifying actual names of files database tables
and printouts
 Adding controls to ensure the process are done
properly.

Partitioning Data Flow Diagram
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 Partitioning is the process of examining a data
flow diagram and detecting how it should be
divided into collection of manual process and
collection of computer programs.

Reason for partitioning DFD
30
 Different user group
 Timing
 Similar tasks
 Efficiency (Report)
 Reliability of data (Credit Card)
 Security (Net Banking)

CRUD Matrix
31

Event Response Table
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Data Flow Diagrams
33

Data Flow Diagram
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Data Flow Diagram
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Use Case and Flow Diagrams
36

In class
example
37

Using data flow diagram

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