Data Flow Diagram (DFD)

Question 1

Represents (visual) the flow of data of a system or a
process.
● Gives insight into the inputs and outputs of each
entity and the process itself.
● Helps to visualize the major steps and data
involved in software-system processes
● Helps to better understand process or system
operations to discover potential problems,
improve efficiency, and develop better processes

Answer 1

Data Flow Diagram (DFD)

Question 2

Main Elements of a DFD

Answer 2

● External Entity
● Process
● Data Store
● Data Flow

Question 3

● (also known as terminators,
sources, sinks, or actors) — are outside systems
that send or receive data to and from the
diagrammed system
● are either the sources or
destinations of information, so they’re usually
placed on the diagram’s edges

Answer 3

External Entity

Question 4

● is a procedure that manipulates the data
and its flow by taking incoming data, changing it,
and producing an output
● can do this by performing computations
and using logic to sort the data or change its flow
of direction
● usually start from the top left of the
DFD and finish on the bottom right of the
diagram

Answer 4

Process

Question 5

● hold information for later use, like a
file of documents that’s waiting to be processed
● Data inputs flow through a process and then
through a data store
● Data outputs flow out of a data store and then
through a process

Answer 5

Data Store

Question 6

● is the path the system’s information
takes from external entities through processes and
data stores
● With arrows and succinct labels, the DFD can
show you the direction of the data flow

Answer 6

Data Flow

Question 7

Common Notation Used in DFD

Answer 7

● Yourdon & De Marco
● Gene & Sarson
● SSADM (Structured Systems Analysis and Design
Method)
● Unified Modeling Language

Question 8

Data can not flow between two entities
○ Data flow must be from entity to a process or a process to
an entity
○ There can be multiple data flows between one entity and
a process

Answer 8

Rule #1

Question 9

Data can not flow between two data
stores
○ Data flow must be from data store to a process or a process
to an data store
○ Data flow can occur from one data store to many process

Answer 9

Rule #2

Question 10

Data can not flow directly from an entity
to data store
○ Data Flow from entity must be processed by a process
before going to data store and vice versa

Answer 10

Rule #3

Question 11

A process must have at least one input
data flow and one output data flow
○ Every process must have input data flow to process the data
and an output data flow for the processed data

Answer 11

Rule #4

Question 12

A data store must have at least one input
data flow and one output data flow
○ Every data store must have input data flow to store the data
and an output data flow for the retrieved data

Answer 12

Rule #5

Question 13

Two data flows can not cross each other

Answer 13

Rule #6

Question 14

All the process in the system must be
linked to minimum one data store or any other
process

Answer 14

Rule #7

Question 15

● depicts how the business operates
● The processes represent the business activities
● The data stores represent the collection of data
regardless of how the data are stored
● It show business controls

Answer 15

Logical DFD

Question 16

● Physical DFD depicts how the system will be
implemented (or how the current system operates)
● The processes represent the programs, program
modules, and manual procedures.
● The data stores represent the physical files and
databases, manual files.
● It show controls for validating input data, for
obtaining a record, for ensuring successful
completion of a process, and for system security

Answer 16

Physical DFD

Question 17

● Top Level view of a system
● Shows the system boundaries, external entities
that interact with the system.
● Major data/information flows between entities and
the system
● Only one process, called PROCESS 0 (zero)
● Label Process 0 is the Name of the System

Answer 17

Context Diagram

Question 18

● Shows the system’s major processes, data flows
and data stores.
● When the context diagram is expanded into Level
0, all the connections that flow into and out of the
Process 0 needs to be retained

Answer 18

Level 0 (Zero) DFD

Question 19

● When there’s a process that may be expanded to
create a more detailed child diagram
● Parent Process – a process in the DFD being
expanded
● Child diagram – a detailed diagram based on the
parent process

Answer 19

Child Diagrams (Lower-Level Diagram)

Question 20

● An iterative process of breaking a system
description down into a finer and finer detail
● Uses a series of increasingly detailed DFDs to
describe a system

Answer 20

Functional Decomposition

Question 21

● The conservation of inputs and outputs to a data
flow process when the process is decomposed to a
lower level
● Ensures that the input and output data flows of the
parent DFD are maintained on the child DFD
*The conservation of inputs and outputs to a data
flow process when the process is decomposed to a
lower level
● Ensures that the input and output data flows of the
parent DFD are maintained on the child DFD

Answer 21

DFD Balancing

Question 22

Guide in Creating DFD’s