Data Flow Diagram (DFD) Flashcards
quize
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
Data Flow Diagram (DFD)
Main Elements of a DFD
● External Entity
● Process
● Data Store
● Data Flow
● (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
External Entity
● 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
Process
● 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
Data Store
● 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
Data Flow
Common Notation Used in DFD
● Yourdon & De Marco
● Gene & Sarson
● SSADM (Structured Systems Analysis and Design
Method)
● Unified Modeling Language
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
Rule #1
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
Rule #2
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
Rule #3
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
Rule #4
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
Rule #5
Two data flows can not cross each other
Rule #6
All the process in the system must be
linked to minimum one data store or any other
process
Rule #7
● 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
Logical DFD
● 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
Physical DFD
● 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
Context Diagram
● 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
Level 0 (Zero) DFD
● 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
Child Diagrams (Lower-Level Diagram)
● 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
Functional Decomposition
● 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
DFD Balancing
Guide in Creating DFD’s
