Data Flow Diagrams

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Data Flow Diagrams
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Data and Process Modeling

• 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
• Level of detail
• Varies between highest summary and lowest detail
• Structured tools enable level of detail to be
  varied

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How Many Levels to Use?

• 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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Data Flow Diagrams (DFDs)

• 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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Context Diagram
Company
Order
Customer
Rejected Order
Despatch Note Goods
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A Complete DFD
Sales
1
Order
Check Credit Rating
Customer
Rejected Order
D1
Credit Rating
Dispatch Note
Accounts
3
Maintain Credit Ratings
2
Warehouse
Dispatch Goods
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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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DFD Symbols

• 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.

• 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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Yourdon
Gane and Sarson
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A Data Flow
Customer
DFD Symbols
An External Entity
Sales
3
A Process
Check Credit Rating
D1
Credit Rating
A Data Store
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The Process Symbol
Unique Number
Where its done
Sales
3
Input Data
Check Credit Rating
Output Data
Whats done
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The data store symbol
D1
Credit Rating
Writing/Updating
Accounts
3
Maintain Credit Rating
Reading
Sales
1
Check Credit Rating
M Manual data Store D Computer File
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The Data Flow Symbol
Use Meaningful names
Customer Balance
Self Evident Data Flows need not be named
D1
Credit Rating
Sales
3
Check Credit Rating
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Physical Resource Flow
Customer
Returned Library Book
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System Boundary
The External Entity Symbol
Customer
A Source and/or sink of data outside the system
boundry
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DFD naming

• Context Diagram
• Diagram 0
• Child diagram (level 1, 2,,n)

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LDFD and PDFD

• 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

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Levelling to avoid complex DFDs, processes can
be grouped into higher level processes
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Dispatch Goods
Process 2.1
Validated Order
1
Dispatch Note
2
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A Complete DFD
Sales
1
Order
Check Credit Rating
Customer
Rejected Order
D1
Credit Rating
Dispatch Note
Accounts
3
Maintain Credit Ratings
2
Warehouse
Dispatch Goods
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Repeated Symbols to avoid crossing lines,
data stores and external entities can be repeated
Customer
Customer
A Duplicated External Entity
D1
Credit Rating
Duplicated Data Store
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DFD Levels
Elementary Functional Description
Level 2
Get cust dets If ordergtcred refer Else
raise order ..
E F D
Level 1
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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.
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Developing Dataflow Diagrams 1. Identify
external entities 2. Draw context diagram 3.
Who/Where does what 4. Identify datastores 5.
Draw diagram
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• External Entities
• Customer
• Context Diagram

order
advice
customer
company
des. note goods
invoice
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What Where/who Receive orders Sales Accumu
late orders Sales Advise availability Sales C
omplete Sales Order Form Sales Despatch
Items Warehouse Write despatch
notes Warehouse Type Invoices Warehouse Send
Invoices Warehouse Datastore Stock file
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customer
Draw DFD
Order
Advice
1
Sales
Stock file
M1
Accumulate orders Advise availability Complete
forms
Sales Order Forms
Warehouse
2
Produce despatch notes Produce Invoices
Invoice
Despatch note goods
customer
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Extensions Maintenance of Stock File Customer
file address, credit etc Payments Accounts dept
invoices, payments etc Accumulate orders
temporary file