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Data Flow Diagramming Rules
• Processes– a process must have at least one input– a process must have at least one output– a process name (except for the context level
process) should be a verb phrase• usually three words: verb, modifier, noun
• on a physical DFD, could be a complete sentence
Data Flow Diagramming Rules
• Data flows– data flows are unidirectional– a data flow may fork, delivering exactly the same data
to two different destinations– two data flows may join to form one only if the
original two are exactly the same– no recursive data flows– data flows (and data stores and sources/sinks) are
labelled with noun phrases
Data Flow Diagramming Rules
• Data stores and sources/sinks– no data flows between two data stores; must be
a process in between– no data flows between a data store and a source
or sink; must be a process in between– no data flows between two sources/sinks
• such a data flow is not of interest, or
• there is a process that moves that data
Practice
• Develop a context diagram for a college course registration system
Course Registration: Context level Diagram
0
CourseRegistration
System
Student
Registrar
Professor
Class Request
Payment
Receipt
Student Schedule
Class roster
Enrollmentstatistics
Level 0 Diagram
• Process is “exploded”
• Sources, sinks, and data flows repeated from context diagram
• Process broken down into subprocesses, numbered sequentially
• Lower-level data flows and data stores added
Course Registration: Current Logical Level 0 Diagram
Student RegistrarProfessor
1.0
RegisterStudent for
Course
D1 Student Class Records
D2 Student Payments
2.0
CollectStudent Fee
Payment
3.0
ProduceStudent
Schedule
4.0
ProduceClassRoster
5.0
ProduceEnrollment
Report
PaymentInformation
Student andCourse Data
StudentClass Record
Student Class Record Student Class Record
Student Class Record
Student Schedule Class RosterEnrollment
Report
StudentClass Request
Receipt
Payment
Child Diagrams
• “Explode” one process in level 0 diagram
• Break down into lower-level processes, using numbering scheme
• Must include all data flow into and out of “parent” process in level 0 diagram
• Don’t include sources and sinks
• May add lower-level data flows and data stores
Course Registration: Current Logical Child Diagram
1.2
Checkfor
Availability
1.1
CheckPrerequisites
Met
1.3
EnrollStudentin Class
D1 Student Class RecordsD5 Course CatalogueD4 Student Transcripts
D3 Semester Schedule
Class Request Valid ClassRequest
Feasible ClassRequest
Available Seats
Available Seats
StudentRecord
Course RecordStudent
and CourseData
Error
Error
Physical DFDs
• Model the implementation of the system
• Start with a set of child diagrams or with level 0 diagram
• Add implementation details– indicate manual vs. automated processes– describe form of data stores and data flows– extra processes for maintaining data
Course Registration: Proposed Physical Child Diagram
1.2
Checkfor
Availability(automated)
1.1
CheckPrerequisites
Met(automated)
1.3
EnrollStudentin Class
(automated)
D1 Semester Enrollment DBD5 Course Catalogue DBD4 Registrar’s Student DB
D3 Semester Schedule DB
Class Request AuthorizedClass Request
Valid ClassRequest
Available Seats
Available Seats
Studentand Course
Data
Student Notified(email)
StudentEmailed
StudentRecord
Course Record
Course Registration: Current Physical Child Diagram
1.2
Checkfor
Availability(Banner)
1.1
CheckPrerequisites
Met(Banner)
1.3
EnrollStudentin Class(Banner)
D1 Semester Enrollment DBD5 Course Catalogue (text)D4 Department Student File
D3 Semester Schedule DB
Class Request AdvisementAuthorization
Feasible ClassRequest
Available Seats
Available Seats
Studentand Course
Data
Student Notified(verbally)
UnavailabilityMessage
StudentFile
Course Description
Practice
• Develop a context diagram for a pizza place (SUNYIT Pizza) that delivers
SUNYIT Pizza: Context Level Diagram
0
CustomerOrder
System
Customer
Cook
Management
Phone Number
Customer Order
Customer Info
DeliveryInformation
WeeklyReport
Cook OrderDeliveryPerson
SUNYIT Pizza: Current Logical Level 0 Diagram
1.0Find
CustomerRecord
7.0Print
WeeklyTotals
6.0SendOrder
to Cook
5.0Add
CustomerRecord
2.0Take
CustomerOrder
3.0Print
DeliveryOrder
Customer
CustomerInfo
PhoneNumber
Customer Order
D1 Customer Master
CustomerRecord
CustomerRecord
CustomerInformation
D2 Customer History
D3 Sales Records
OrderInformation
OrderInformation
CustomerHistory
DeliveryInformation
CustomerCustomerOrder
Cook
CookOrder
Management
Sales Info
Weekly Report
DiscountInfo
DeliveryPerson
SUNYIT Pizza: Current Logical Child Diagram
3.1
DetermineCustomerDiscount
3.2
RecordDiscount
3.3
PrintDelivery
Instructions
OrderInformation
DiscountAmount
DeliveryInformation
D2 Customer History
D3 Sales Records
CustomerHistory
DiscountInformation
CustomerInformation
SUNYIT Pizza: Current Logical Child Diagram
5.1
RecordCustomer
Information
5.2
StoreCustomer
Record
D1 Customer Master
Customer Information RawCustomer
Information
CustomerRecord
SUNYIT Pizza: Physical Child Diagram
5.3Clerk
VisuallyConfirmsCust. Info.
5.1Clerk Types
CustomerInformation
5.2System
ValidatesCustomer
Information
5.4Format
CustomerRecord
PhonedCustomer
InformationRecordedCustomer
Information
Valid CustomerInformation
SyntaxErrors
CancelledTransaction
New CustomerInformationD1 Customer DB
CustomerRecord
PhoneNumber
SUNYIT Pizza: Current Physical Level 0 Diagram
1.0Clerk FindsCustomer
Row
7.0Mgr Prints
WeeklyTotals(batch)
6.0Clerk Sends
Orderto Cook(paper)
5.0Clerk AddsCustomer
Row
2.0Clerk TakesCustomer
Order(by phone)
3.0System Prints
DeliveryOrder
Customer
PhonedCustomer
Info
PhoneNumber
PhonedCustomer Order
D1Customer Spreadsheet
CustomerRecord
CustomerRecord
CustomerInformation
D2 Customer History DB
D3 Sales Records File
Copy ofOrder Slip
Customer& Order
Info
CustomerHistoryRecord
DeliveryPrintout
Customer
CookCopy of
order slipManagement
Copies ofOrder Slips
Weekly ReportPhone #
Cust.Info.
DeliveryPerson
8.0Mgr Updates
CustomerHistory
(nightly)Copies of
Order Slips& Del. Printouts
CustomerHistoryRecord
PhonedCustomer
Order
SUNYIT Pizza: Proposed Physical Level 0 Diagram
1.0System Finds
CustomerRecord
7.0System Prints
WeeklyTotals(batch)
5.0Clerk AddsCustomer
Record
2.0Clerk Enters
CustomerOrder
(by phone)
3.0System Prints
DeliveryOrder
Customer
PhonedCustomer
Info
PhoneNumber
PhonedCustomer Order
D1 Customer DB
CustomerRecord
CustomerRecord
CustomerInformation
D2 Customer History DB
D3 Sales DB
OrderInfo
OrderInfo
CustomerHistoryRecord
DeliveryPrintout
Cook Management
SalesRecords
Weekly ReportPhone #
Cust.Info.
DeliveryPerson
D3 Sales DBOrderInfo
DiscountInfo
Data Flow Diagramming Rules
• Processes– a process must have at least one input– a process must have at least one output– a process name (except for the context level
process) should be a verb phrase• usually three words: verb, modifier, noun
• on a physical DFD, could be a complete sentence
1.0
GatherData
2.0
CompileStatistics
Demographic Data
3.0
AnalyzeResponses
SurveyResponses
FinalReport
2.0
VisaAuthorization
2.0
TotalRecords
2.0
QAProcess
2.0
CheckCustomer
Credit
2.0
TotalSales
Records
2.0
InspectFinishedProducts
BETTER
BETTER
BETTER
Data Flow Diagramming Rules
• Data stores and sources/sinks– no data flows between two data stores; must be
a process in between– no data flows between a data store and a source
or sink; must be a process in between– no data flows between two sources/sinks
• such a data flow is not of interest, or
• there is a process that moves that data
2.1
StoreCustomer
Data
CustomerInformation
D1 Customer Data
D2 Customer Preferences
CustomerData
CustomerPreferences
2.1
StoreCustomer
Data
CustomerInformation
D1 Customer Data
D2 Customer Preferences
CustomerData Customer
Preferences
2.1
StoreCustomer
Data
CustomerInformation
D1 Customer Data
D2 Customer Preferences
CustomerData
CustomerPreferences
2.1
StoreCustomer
Data
CustomerInformation
D1 Customer Data
D2 Customer Preferences
CustomerData
CustomerPreferences
2.2
ExtractCustomer
Preferences
CustomerData
D1 Customer Data
CustomerData
2.0
StoreCustomer
Data
D1 Customer Data
CustomerData
Customer
CustomerInformation
Customer
0
MedicalBillingSystem
Doctor
Patient
Diagnosis
ServiceInformation
Bill
Data Flow Diagramming Rules
• Data flows– data flows are unidirectional– a data flow may fork, delivering exactly the same data
to two different destinations– two data flows may join to form one only if the
original two are exactly the same– no recursive data flows– data flows (and data stores and sources/sinks) are
labelled with noun phrases
2.0
TotalDailySales
1.0
TakeCustomer
Order
3.0
PrintDelivery
Instructions
CustomerOrder
OrderInformation
OrderTotal
2.0
TotalDailySales
1.0
TakeCustomer
Order
3.0
PrintDelivery
Instructions
OrderInformation
OrderTotal
2.0
LookupCustomer
Record
1.0
TakeCustomer
Order
3.0
PrintDelivery
Instructions
CustomerOrder
CustomerAddress
CustomerInformation
2.0
LookupCustomer
Record
1.0
TakeCustomer
Order
3.0
PrintDelivery
Instructions
CustomerOrder
CustomerAddress
1.0
CalculateWeekly
Sales
DailySales
CumulativeTo-Date
Sales
Data Flow Diagramming Guidelines
• The inputs to a process are different from the outputs
• Every object in a DFD has a unique name
1.0
ValidateCustomer
Data
1.0
ValidateCustomer
Data
CustomerData
CustomerData
ValidCustomer
Data
CustomerData
2.0
TakeCustomer
Order
1.0
GetCustomer
Data
3.0
ProcessCustomer
Order
CustomerData
CustomerData
Order
2.0
TakeCustomer
Order
1.0
GetCustomer
Data
3.0
ProcessCustomer
Order
CustomerData
Order
1.0
GetCustomer
Data
2.0
TakeCustomer
Order
3.0
ValidateCustomer
Data
CustomerData
Only if these are exactly the same
CustomerData
Data Flow Diagramming Guidelines
• A data flow at one level may be decomposed at a lower level
• All data coming into and out of a process must be accounted for
• On low-level DFDs, new data flows can be added to represent exceptional situations
1.0
GetCustomerAddress
CustomerInformation
CustomerAddress
1.2
LookupCustomerAddress
1.1
GetCustomer
Phone
1.3
RequestCustomerAddress
CustomerPhone
CustomerAddress
CustomerPhone
CustomerAddress
1.0
GetCustomerAddress
CustomerInformation
CustomerAddress
1.2
LookupCustomerAddress
1.1
GetCustomer
Phone
1.3
RequestCustomerAddress
CustomerPhone
CustomerAddress
CustomerPhone
CustomerAddress
Invalid PhoneNumber Message
Data Elements
• Indivisible pieces of data
• Data flows and data stores are made up of data elements
• Like attributes on an ER diagram
• The data elements of a data flow flowing in or out of a data store must be a subset of the data elements in that data store
1.0
CalculateGrossPay
D2 Employee Time File
Employee
Employee
D1 Employee Master
D3 Check Reconciliation
D1 Employee Master
2.0
CalculateWithholding
Amount
3.0
CalculateNetPay
4.0
PrintEmployeePaycheck
HoursWorked
EmployeeTime
Record
GrossPay
Withholding
NetPay
EmployeeRecord
EmployeeRecord
CheckReconciliation
Record EmployeePaycheck
1.0
CalculateGrossPay
D2 Employee Time File
Employee
Employee
D1 Employee Master
D3 Check Reconciliation
D1 Employee Master
2.0
CalculateWithholding
Amount
3.0
CalculateNetPay
4.0
PrintEmployeePaycheck
HoursWorked
EmployeeTime
Record
GrossPay
WithholdingAmount
NetPay
EmployeeRecord
EmployeeRecord
CheckReconciliation
Record
EmployeePaycheck
5.0
CreateTime
RecordEmployee
Time Record
Number ofDependents
GrossPay
D4Withholding Tables
WithholdingRates
6.0
ReconcilePay
Check
PaycheckInformation
DFDs and ERDs
• DFDs and ERDs are both used to model systems, but they show two very different perspectives on the system
• A DFD shows what the system does as well as the data that the system manipulates
• An ERD shows only the data that the system manipulates.
DFDs and ERDs (cont.)• Entities on an ERD often (but not always) correspond to
data stores on a DFD
• Attributes on an ERD usually correspond to data elements (listed in the data dictionary) that make up the data store and data flows on a DFD
• Relationships on an ERD do not correspond to processes on a DFD.
• Sources and sinks on a DFD usually do not show up as entities on an ERD
Example DFD and ERD
Cook Customer
Inventory
PlacesOrder
Name Hours Name
Address
Item Quantity
DFD
Incorrect ERD
Customer
CookInventory
Processing
1.0
TakeOrder
2.0
Convert Orderto CookingInstructions
3.0
Convert Orderto Ingredient
List
ProcessedOrder
D1 Order Log
CookingInstructions
Ingredients
Example DFD and ERD
Customer
CookInventory
Processing
1.0
TakeOrder
2.0
Convert Orderto CookingInstructions
3.0
Convert Orderto Ingredient
List
ProcessedOrder
D1 Order Log
CookingInstructions
Ingredients
Correct ERD
DFDOrder
Item
Ingredient
CookingInstructions
Contains
Includes
Requires
OrderId
Date
Time
ItemId ItemName
StepId Description
Description
ItemQuantity
IngredientQuantity
Index
