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Data Flow Diagrams (DFDs)Data Flow Diagrams (DFDs)
Creating data flow diagrams to understand business
processes.

Data Flow Diagrams (DFDs)Data Flow Diagrams (DFDs)
?Data flow diagram
(DFD) is a picture of
the movement of data
between external
entities and the
processes and data
stores within a
system

DFD Symbols (Gane & Sarson)DFD Symbols (Gane & Sarson)
Process
Data Flow
Data Store
Source/Sink (External Entity)

ProcessProcess
?Work or actions performed on data (inside the
system)
?Labels should be verb phrases
?Receives input data and produces output

Rule 1: ProcessRule 1: Process
?Can have more than one outgoing data flow or
more than one incoming data flow

Rule 2: ProcessRule 2: Process
?Can connect to any other symbol (including
another process symbol)

Process: Correct/Incorrect?Process: Correct/Incorrect?

Data StoreData Store
?Is used in a DFD to represent data that the
system stores
?Labels should be noun phrases

Rule: Data StoreRule: Data Store
?Must have at least one incoming and one
outgoing data flow

Source/Sink (External Entity)Source/Sink (External Entity)
?External entity that is origin or destination of
data (outside the system)
?Is the singular form of a department, outside
organisation, other IS, or person
?Labels should be noun phrases
? Source �C Entity that supplies data to the
system
? Sink �C Entity that receives data from the
system

Rule: Source/SinkRule: Source/Sink
?Must be connected to a process by a data flow

Rules for Using DFD SymbolsRules for Using DFD Symbols
?Data Flow That Connects
YES NO
A process to another process
A process to an external entity
A process to a data store
An external entity to another external entity
An external entity to a data store
A data store to another data store

Context DiagramContext Diagram
?Top-level view of IS
?Shows the system boundaries, external entities that
interact with the system, and major information
flows between entities and the system.
?Example: Order system that a company uses to
enter orders and apply payments against a
customer��s balance

Level-0 DFDLevel-0 DFD
?Shows the system��s major processes, data flows,
and data stores at a high level of abstraction
?When the Context Diagram is expanded into DFD
level-0, all the connections that flow into and out
of process 0 needs to be retained.

Lower-Level DiagramsLower-Level Diagrams
?Functional Decomposition
? An iterative process of breaking a system description
down into finer and finer detail
? Uses a series of increasingly detailed DFDs to
describe an IS
?Balancing
? The conservation of inputs and outputs to a data flow
process when that 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

Strategies for Developing DFDsStrategies for Developing DFDs
?Top-down strategy
? Create the high-level diagrams (Context
Diagram), then low-level diagrams (Level-0
diagram), and so on
?Bottom-up strategy
? Create the low-level diagrams, then higher-
level diagrams

Exercise:
Precision Tools sells a line of high-quality woodworking tools.
When customers place orders on the company��s Web site, the
system checks to see if the items are in stock, issues a status
message to the customer, and generates a shipping order to the
warehouse, which fills the order. When the order is shipped, the
customer is billed. The system also produces various reports.
? Draw a context diagram for the order system
? Draw DFD diagram 0 for the order system

Identify Entities,Process,Data Stores & Data FlowIdentify Entities,Process,Data Stores & Data Flow
? Entities
? Customer
? Warehouse
? Accounting
? Processes
? 1.0 Check Status
? 2.0 Issue Status Messages
? 3.0 Generate Shipping Order
? 4.0 Manage Accounts Receivable
? 5.0 Produce Reports
? Data Stores
? D1 Pending Orders
? D2 Accounts Receivable
? Data Flows
? Order
? In-Stock Request
? Order Data
? Status Data
? Status Message
? Shipping Order
? Order Data
? Invoice
? Shipping Confirmation
? Payment
? Accounting Data
? Accounts Receivable Data
? Order Data
? Inventory Reports
1.0
2.0
3.0
4.0
5.0

Context
Diagram of
Order
System

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