Transcript Data Flow Diagrams - IST Akprind Yogyakarta

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During systems development both processes and
data must be modeled
◦ Data modeling describes data used by system
◦ Process modeling describes processes carried out by
system
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Level of detail
◦ Varies between highest summary and lowest detail
◦ Structured tools enable level of detail to be varied
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Restrict a single DFD to no more than six to eight
processes
Use another tool to document the lowest level of
detail but use no more than a single page.
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Graphic representation of a system that uses a small
number of symbol shapes to illustrate how data
flows through interconnected processes
◦ Most natural way to document processes
◦ Emphasis on processes rather than data
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Data Flow Diagrams (DFDs) show:
•The processes within the system
•The datastores (files) supporting its operation
•The information flows within it
•The system boundary
•Interactions with external entities
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DFDs consist of four symbols
1) Environmental elements called terminators / external
entity
 Person
 Organization
 Another system
2) Processes which transform inputs to outputs
 Labeled with verb and object
 Also labeled with system or computer program name
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DFD symbols [cont.]
◦ Data flows which consist of logically related data elements
that travel from one point or process to another. In other
words, data in motion.
 Structures
 Diverge
 Converge
◦ Data stores which are data repositories. In other words,
data at rest.
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A Data Flow
Customer
3
An External Entity
Sales
A Process
Check Credit
Rating
D1
Credit
Rating
A Data Store
DFD Symbols
The Process Symbol
Where it’s done
Unique Number
3
Input
Data
Sales
Check Credit
Rating
What’s done
Output Data
The data store symbol
Writing/Updating
3
D1
Credit
Rating
Accounts
Maintain
Credit Rating
Reading
1
M = Manual data Store
D = Computer File
Sales
Check Credit
Rating
The Data Flow Symbol
Use Meaningful
names
Customer Balance
Self Evident Data Flows need
not be named
3
D1
Sales
Check Credit
Rating
Credit
Rating
Physical Resource Flow
Customer
Returned
Library Book
The External Entity Symbol
Customer
A Source
and/or sink of
data outside
the system
boundry
System Boundary
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Context Diagram
Diagram 0
Child diagram (level 1, 2,…,n)
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DFD dikelompokkan menjadi 2:
◦ Logical DFD
 Fokus pada bisnis dan bagaimana bisnis berjalan
 How the system will be constructed
◦ Physical DFD
 How the system will be implemented
 Include hardware, software, files, people yang terlibat
dalam sistem
Levelling – to avoid complex DFDs, processes can be grouped into
higher level processes
2
Dispatch Goods
Process
2.1
Validated
1
Order
Dispatch
Note
2
A Complete DFD
1
Sales
Order
Check Credit
Rating
Customer
Rejected
Order
D1
Dispatch
Note
3
2
Warehouse
Dispatch
Goods
Accounts
Maintain Credit
Ratings
Credit
Rating
Repeated Symbols – to avoid crossing lines, data
stores and external entities can be repeated:
Customer
Customer
D1
Credit
Rating
A Duplicated External Entity
Duplicated Data Store
DFD Levels
Elementary
Functional
Level 2
Description
Get cust dets
If order>cred
refer
Else
raise order
…..
EFD
Level 1
Sample
A wines and spirits wholesaler stocks a range of approximately 400
different lines and delivers by van on regular weekly runs to customers
who are mainly off-licenses and clubs. The majority of orders are
received by telephone and any one customer may place several orders
during the week which must be accumulated and delivered in one
consignment. When a customer telephones he expects to be advised on
the availability of an item requested and, if not in stock, the alternatives
that are available. At present, sales order forms are filled in by the
telephone salesmen and sent to the warehouse where they are used for
the despatch of the items. Hand-written despatch notes are used as the
basis of the invoices which are typed and sent by post sometime later.
Prepare a dataflow diagram (DFD) which represents the above system.
Developing Dataflow Diagrams
1. Identify external entities
2. Draw context diagram
3. Who/Where does what
4. Identify datastores
5. Draw diagram
External Entities
1. Customer
Context Diagram
order
advice
customer
des. note + goods
invoice
company
What
Where/who
Receive orders
Sales
Accumulate orders
Sales
Advise availability
Sales
Complete Sales Order Form
Sales
Despatch Items
Warehouse
Write despatch notes
Warehouse
Type Invoices
Warehouse
Send Invoices
Warehouse
Datastore
Stock file
customer
Draw DFD
Order
Advice
1
Sales
M1
Accumulate orders
Advise availability
Complete forms
Sales Order Forms
2
Warehouse
Produce despatch
notes
Produce Invoices
Despatch note +
goods
Invoice
customer
Stock file
Extensions
Maintenance of Stock File
Customer file – address, credit etc
Payments
Accounts dept – invoices, payments etc
Accumulate orders – temporary file