Unit02 - Software Analysis And Design DFD - Data Flow Diagram Software Engineering Diploma in Computer/IT Engineering, Gujarat Technological University, Gujarat, India

1. DFD:
Data Flow Diagram
by:
Dr. Bharat V. Chawda
Computer Engineering Department,
BBIT, VVNagar, Gujarat, India
1

2. Overview
 A Concept
 Primitive Symbols
 Context Diagram
 Level 1 Diagram
 Decomposition
 Example
 Do’s and Don’ts
 Shortcomings
2

3. A Concept: Simple Example
 RMS: Root Mean Square
3
RMS
Calculator
0
User
I/P Data
rms
Validate
input
1
Compute
RMS
2
Valid Data
Display
result
3
rms rms
Further Decomposition…
I/P Data

4. Concept
 “A graphical representation of the flow of
data through an information system, modelling
its process aspects.”
 “A hierarchical graphical model of a system
that shows –
 The different processing activities / functions that
the system performs, and
 The data interchange among those functions.”
 Also known as the Bubble Chart
4

5. Concept
 Shows:
 What data is Input; Who generates it: Source
 What data is O/P; Who receives it: Destination/Sink
 What processing is performed on data; by whom: Proc
 Where data come from and go to: Data Flow
 What data is stored; where: Data Store
 Does not show:
 Timing of processes: Executed in parallel or sequence
 Conditions: based on which functions may or may not
get executed
 Control flow / Algorithmic details
 That’s why: Different from Flowchart
5

6. Concept
 Why Popular?
 Easy to understand by technical and non-technical
persons
 Can provide high level system overview; with
boundaries and connections to other systems
 Can provide a detailed representation of system
components
 Uses limited number of primitive symbols (only four)
 Provides hierarchy of DFDs – Reduces complexity using
abstraction at each level
 Top level: Most abstract: Context Diagram / Level 0 Diagram
 Next level: Level 1 Diagram
 Further levels: Level 2, 3, 4…
6

7. Primitive Symbols for DFD
 Process / Function: Circle,
Rounded Rectangle
 Actions performed on data:
Transformed, Stored, or Distributed
 Annotated with number and name of
function
 Name starts with verb (Except context
level diagram)
 Data Flow: Directed arc, Arrow
 Single piece of data or logical
collection of data
 Annotated with name/description of
data
7

8. Primitive Symbols for DFD
 External Entity: Rectangle
 Source and/or Sink
 Origin and/or Destination of the data
 External, cos outside the system
 Annotated with name (Noun)
 Data Store: Open rectangle,
parallel lines
 Data structure, File, Table, Database
 Annotated with corresponding names
of data items
8

9. Context or Level 0 Diagram
 Concept:
Most abstract representation of the system
Highest level or simplest representation of system
Entire system as single bubble – annotated with
software name (noun is used for naming bubble)
Represents the context in which system would
exist – external entities, data input to the system,
data output from the system
9

10. Context or Level 0 Diagram
 Main steps:
Identify where data is captured from: Source
Identify where data is distributed to: Destination
Describe the overall process
Map these out in a diagram using the correct
symbols
Link them with data flows that are labelled
10

11. Level 1 Diagram
 Concept:
Represents high level functions of the system –
derived based on functional requirements from
SRS
3 to 7 bubbles – each representing single high
level function
Input data to these functions
Output data from these functions
External entities can be avoided
Data store can be introduced at this level or at
next levels
11

12. Level 1 Diagram
 Main steps:
 Identify and draw the processes that make up the Level 0
process: High level functions
 Allocate descriptions to these processes
 Lay out the sources/sinks and data flows from the
Level 0 diagram
 Draw in any data stores used in the process
 Link the new processes and data stores with named data
links: Data flows
12

13. Decomposition
 Concept:
Also knows as factoring or exploding a bubble
Bubbles are decomposed into sub-functions at
the successive levels of the DFD model
Decomposition into 3 to 7 bubbles
Too few: superfluous, redundant, trivial
Too many: makes DFD model hard to understand
How far: until function can be described using
simple algorithm or instructions
13

14. Decomposition
 Numbering:
Numbering:
Context Level DFD: 0
Level 1 DFD: 1,2,3…
Level 2 DFD: 1.1, 1.2,…, 2.1,2.2,…
 Balancing:
The data that flow into or out of a bubble must
match the data flow at the next level of DFD.
14

15. Decomposition/Level ‘n’ Diagram
 Main steps:
 Identify and draw the processes that make up the Level
n-1 process
 Allocate descriptions to these processes
 Lay out all the data flows from the Level n-1 diagram
 Draw in any data stores used in the process
 Link the new processes and data stores with named data
links: Data flows
15

16. Ex: Food Order System
 Description
 Customer provides order.
 System produces receipt by referring order and gives to
customer.
 Order is also sent to kitchen department.
 Based on order, “Goods sold” and “Inventory” files are
updated.
 Reports for the top management regarding sales,
inventory depletion (income, expenditure) are generated.
16

17. Context or Level 0 Diagram
 Main steps:
Identify where data is captured from
Identify where data is distributed to
Describe the overall process
Map these out in a diagram using the
correct symbols
Link them with data flows that are labelled
17

18. Context or Level 0 Diagram
18
CUSTOMER

19. Context or Level 0 Diagram
 Main steps:
Identify where data is captured from
Identify where data is distributed to
Describe the overall process
Map these out in a diagram using the
correct symbols
Link them with data flows that are labelled
19

20. Context or Level 0 Diagram
20
CUSTOMER KITCHEN
RESTAURANT
MANAGER

21. Context or Level 0 Diagram
 Main steps:
Identify where data is captured from
Identify where data is distributed to
Describe the overall process
Map these out in a diagram using the
correct symbols
Link them with data flows that are labelled
21

22. Context or Level 0 Diagram
22
Food
Ordering
System
0
CUSTOMER KITCHEN
RESTAURANT
MANAGER

23. Context or Level 0 Diagram
 Main steps:
Identify where data is captured from
Identify where data is distributed to
Describe the overall process
Map these out in a diagram using the
correct symbols
Link them with data flows that are
labelled
23

24. Disclaimer
24
Food
Ordering
System
0
CUSTOMER KITCHEN
RESTAURANT
MANAGER
Receipt
Food Order
Management
Reports
Customer Order

25. Level 1 Diagram
 Main steps:
 Identify and draw the processes that make up the
Level 0 process
 Allocate descriptions to these processes
 Lay out the sources/sinks and data flows from the Level 0
diagram
 Draw in any data stores used in the process
 Link the new processes and data stores with named data
links
25

26. Level 1 Diagram
26
1.0
Receive and
transform
Customer
Food Order
3.0
Update
Inventory
file
2.0
Update
Goods Sold
file
4.0
Produce
Management
Reports

27. Level 1 Diagram
 Main steps:
 Identify and draw the processes that make up the Level 0
process
 Allocate descriptions to these processes
 Lay out the sources/sinks and data flows from the
Level 0 diagram
 Draw in any data stores used in the process
 Link the new processes and data stores with named data
links
27

28. Level 1 Diagram
28
1.0
Receive and
transform
Customer
Food Order
3.0
Update
Inventory
file
2.0
Update
Goods Sold
file
4.0
Produce
Management
Reports
Receipt
Customer Order
CUSTOMER KITCHEN
Food Order
RESTAURANT
MANAGER
Management
Reports

29. Level 1 Diagram
 Main steps:
 Identify and draw the processes that make up the Level 0
process
 Allocate descriptions to these processes
 Lay out the sources/sinks and data flows from the Level 0
diagram
 Draw in any data stores used in the process
 Link the new processes and data stores with named data
links
29

30. Level 1 Diagram
30
1.0
Receive and
transform
Customer
Food Order
3.0
Update
Inventory
file
2.0
Update
Goods Sold
file
4.0
Produce
Management
Reports
Receipt
Customer Order
CUSTOMER KITCHEN
Food Order
RESTAURANT
MANAGER
Management
Reports
D1 Goods Sold File D2 Inventory File

31. Level 1 Diagram
 Main steps:
 Identify and draw the processes that make up the Level 0
process
 Allocate descriptions to these processes
 Lay out the sources/sinks and data flows from the Level 0
diagram
 Draw in any data stores used in the process
 Link the new processes and data stores with
named data links
31

32. Level 1 Diagram
32
1.0
Receive and
transform
Customer
Food Order
3.0
Update
Inventory
file
2.0
Update
Goods Sold
file
4.0
Produce
Management
Reports
Receipt
Customer Order
CUSTOMER KITCHEN
Food Order
RESTAURANT
MANAGER
Management
Reports
Goods
Sold
Inventory
Data
Goods
Sold Data
Inventory
Data
Daily Goods Sold Amount Daily Inventory Depletion Amount
D1 Goods Sold File D2 Inventory File

33. Level ‘n’ Diagram
 Main steps:
 Identify and draw the processes that make up the Level
n-1 process
 Allocate descriptions to these processes
 Lay out the sources/sinks and data flows from the Level
n-1 diagram
 Draw in any data stores used in the process
 Link the new processes and data stores with named data
links
33

34. Level 2 Diagram
34
4.0
Produce
Management
Reports
Management
Reports
Daily Goods Sold Amount Daily Inventory Depletion Amount
4.1
Access Goods
Sold and
Inventory Data
4.2
Aggregate
Goods Sold
and Inventory
Data
4.3
Prepare
Management
Reports
Daily
Goods
Sold
Amount
Daily Inventory
Depletion Amount
Goods
Sold data
Inventory
Data
Aggregated
Data
Management
Reports

35. Level 3 Diagram
35
4.3
Prepare
Management
Reports
Aggregated
Data
Management
Reports
4.3.1
Format
Management
Reports
Aggregated
Data
4.3.2
Print
Management
Reports
Formatted
Data
Management
Reports

36. Do’s and Don’ts
36


Processes must have both Inputs and Outputs
No process can have only Inputs or only Outputs

37. Do’s and Don’ts
37

 All flows to Data store must move through a
Process


38. Do’s and Don’ts
38

 All flows to External Entity must move through
a Process


39. Shortcomings of DFD
 Can be Imprecise
 May not capture the entire functionality
 What happens if inputs are wrong; if book not found
 Control aspects not defined
 Order: inputs are consumed, output r produced: X
 Order: different processes are executed: X
 Decomposition: Subjective
 How to arrive at successive level; Up to how much level:
subjective; depends upon analyst
 Same problem  Multiple DFDs possible
 Decomposition: No specific guidance
39

40. To be continued…
40