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
2
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)
4

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
7

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)
11
 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)
12

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….)
14
 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
23

Developing Logical Flow
Diagrams
 Advantages
 Better communication w/users
 Stable systems
 Understanding of business
 Flexibility and maintenance
 Identify redundancies
24

Developing Physical DFD
25
 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
29
 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
32

Data Flow Diagrams
33

Data Flow Diagram
34

Data Flow Diagram
35

Use Case and Flow Diagrams
36

In class
example
37

Using data flow diagram

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