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DFD examples
1
Creating DFDs
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Define Entities • External entities represent
persons, processes or machines which produce data to be used by the system or receive data that is output by the system
• Examples: Student, Customer, Client
Define Processes• Processes are discrete actions
that transform input data to output data
• Examples: Create Student Record, Calculate Purchase Cost, Register Client
Student
2.1
Create Student Record
Creating DFDs (cont’d)Define Data Stores
• Data stores are temporary or permanent repositories of information that are inputs to or outputs of processes
• Examples: Student Master, Client List
Define Data Flows• Data flows represent the
transfer of data over time from one “place” (entity, process, data store) to another
• Examples: New Student Information (from Student, to Student Master)
3
New Student Information
Student Master
D3
Creating DFDs (cont’d)Define the System
• A system is the collection of all business processes which perform tasks or produce outputs we care about. It is “what happens.”
• The system is a single process, connected to external entities
• Represented in a “Context Diagram”
Define Subsystems• A subsystem gives a more
detailed view individual processes contained in the context diagram
• Includes data stores, more elementary processes
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DFDs Created by Top-Down AnalysisCreate a narrative: description of
systemCreate a Context Diagram that
contains a single process (“the system”) and all entities which share data with the system
Explode the “parent” context diagram to produce a Diagram 0 (“child”) DFD
Create Diagram 1, 2, …, n DFDs that represent “explosions” of Diagram 0, 1, …, n-1 DFDs until a diagram has only “primitive” processes
Create process descriptions to be implemented by application programs: queries, macros, reports, programming languages
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Context Diagram
Diagram 0 DFD
Diagram 1 DFDs
Diagram n DFDs
Narrative
E-R Diagram Process Descriptions
Where to Begin Creating DFDsStart with the data flow from an external entity
and work forwards
Start with the data flow to an external entity and work backwards
Examine the data flows into or out of a data store
Examine data flows, entity connections and data stores associated with a particular process
Note fuzzy, ill-defined areas of the system for further clarification
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What to Avoid in DFDs
Making the data flow diagram too cluttered (e.g. 9 processes)
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4
Perform Repair
Processes with no outputs or no inputs
1 2 3Many processes with a single input and output (linear flow)
Processes whose inputs are obviously inadequate to yield
outputs
Having data flows terminate at data stores
Connecting data stores directly to each other
Courses StudentsClass List
Connecting entities to anything other than processes
Payroll Department
Employees
Process A
Process B
Process C
Creating Data Flow Diagrams
Lemonade Stand Example
Creating Data Flow Diagrams
Steps:
1. Create a list of activities
• Old way: no Use-Case Diagram
• New way: use Use-Case Diagram
2. Construct Context Level DFD(identifies sources and sink)
3. Construct Level 0 DFD (identifies manageable sub processes )
4. Construct Level 1- n DFD (identifies actual data flows and data stores )
Example
The operations of a simple lemonade stand will be used to demonstrate the creation of dataflow diagrams.
Creating Data Flow Diagrams
1. Create a list of activitiesExample
Think through the activities that take place at a lemonade stand.
Customer OrderServe ProductCollect PaymentProduce ProductStore Product
Creating Data Flow Diagrams
Example
Also think of the additional activities needed to support the basic activities.
Customer OrderServe ProductCollect PaymentProduce ProductStore ProductOrder Raw MaterialsPay for Raw MaterialsPay for Labor
1. Create a list of activities
Creating Data Flow Diagrams
Example
Group these activities in some logical fashion, possibly functional areas.
Customer OrderServe ProductCollect Payment
Produce ProductStore Product
Order Raw MaterialsPay for Raw Materials
Pay for Labor
1. Create a list of activities
Creating Data Flow Diagrams
0.0Lemonade
SystemEMPLOYEECUSTOMER
PayPayment
Order
Context Level DFD
Example
Create a context level diagram identifying the sources and sinks (users).
Customer OrderServe ProductCollect Payment
Produce ProductStore Product
Order Raw MaterialsPay for Raw Materials
Pay for Labor
VENDOR
PaymentPurchase Order
Production Schedule
Received GoodsTime Worked
Sales Forecast
2. Construct Context Level DFD(identifies sources and sink)
Product Served
Creating Data Flow Diagrams
Level 0 DFD
Example
Create a level 0 diagram identifying the logical subsystems that may exist.
Customer OrderServe ProductCollect Payment
Produce ProductStore Product
Order Raw MaterialsPay for Raw Materials
Pay for Labor
3. Construct Level 0 DFD (identifies manageable sub processes )
2.0Production EMPLOYEEProduction
Schedule
1.0Sale
3.0Procure-
ment
Sales Forecast
Product Ordered
CUSTOMER
Pay
Payment
Customer Order
VENDOR
Payment
Purchase Order Order Decisions
Received Goods
Time Worked
Inventory
Product Served
4.0Payroll
Creating Data Flow Diagrams
Level 1 DFD
Example
Create a level 1 decomposing the processes in level 0 and identifying data stores.
4. Construct Level 1- n DFD (identifies actual data flows and data stores )
1.3Produce
Sales Forecast Sales ForecastPayment
Customer OrderServe ProductCollect Payment
Produce ProductStore Product
Order Raw MaterialsPay for Raw Materials
Pay for Labor
1.1Record Order
Customer Order
ORDER
1.2Receive Payment
PAYMENT
Severed Order
Request for Forecast
CUSTOMER
Creating Data Flow Diagrams
Level 1 DFD
Example
Create a level 1 decomposing the processes in level 0 and identifying data stores.
4. Construct Level 1 (continued)
Customer OrderServe ProductCollect Payment
Produce ProductStore Product
Order Raw MaterialsPay for Raw Materials
Pay for Labor
2.1Serve
Product
Product Order
ORDER
2.2Produce Product
INVENTORTY
Quantity Severed
Production Schedule
RAW MATERIALS
2.3Store
Product
Quantity Produced & Location Stored
Quantity Used
Production Data
Creating Data Flow Diagrams
Level 1 DFD
Example
Create a level 1 decomposing the processes in level 0 and identifying data stores.
4. Construct Level 1 (continued)
Customer OrderServe ProductCollect Payment
Produce ProductStore Product
Order Raw MaterialsPay for Raw Materials
Pay for Labor
3.1Produce Purchase
Order
Order DecisionPURCHASE
ORDER
3.2Receive
Items
Received Goods
RAW MATERIALS
3.3Pay
Vendor
Quantity Received
Quantity On-Hand
RECEIVED ITEMS
VENDOR
Payment Approval
Payment
Creating Data Flow Diagrams
Level 1 DFD
Example
Create a level 1 decomposing the processes in level 0 and identifying data stores.
4. Construct Level 1 (continued)
Time Worked
Customer OrderServe ProductCollect Payment
Produce ProductStore Product
Order Raw MaterialsPay for Raw Materials
Pay for Labor
4.1Record Time
Worked
TIME CARDS
4.2Calculate
Payroll
Payroll Request
EMPLOYEE
4.3Pay
Employee
Employee ID
PAYROLL
PAYMENTS
Payment Approval
Payment
Unpaid time cards
Process Decomposition
4.1Record Time
Worked
4.2Calculate
Payroll
4.3Pay
Employee
3.1Produce Purchase
Order
3.2Receive
Items
3.3Pay
Vendor
2.1Serve
Product
2.2Produce Product
2.3Store
Product
1.1Record Order
1.2Receive Payment
2.0Production
1.0Sale
3.0Procure-
ment
4.0Payroll
0.0Lemonade
System
Level 0 Level 1Context Level
DFD Example: Bus Garage RepairsBuses come to a garage for repairs. A mechanic and helper perform the repair, record the reason for
the repair and record the total cost of all parts used on a Shop Repair Order.
Information on labor, parts and repair outcome is used for billing by the Accounting Department, parts monitoring by the inventory management computer system and a performance review by the supervisor.
Key process (“the system”): performing repairs and storing information related to repairs
External Entities: Bus, Mechanic, Helper, Supervisor, Inventory Management System, Accounting Department, etc.
Processes: Record Bus ID and reason for repair Determine parts needed Perform repair Calculate parts extended and total cost Record labor hours, cost
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DFD Example: Bus Garage Repairs (cont’d)Data stores:
Personnel file Repairs file Bus master list Parts list
Data flows: Repair order Bus record Parts record Employee timecard Invoices
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Bus
Mechanic
Helper0
Bus Repair Process
Supervisor
Accounting
Bus Garage Context Diagram
Mechanical problem to be repaired
Labor
Labor
Fixed mechanical problems
Inventory Management
System
Repair summary
List of parts used
Labor, parts cost details