Data Flow Diagram
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Transcript of Data Flow Diagram
![Page 1: Data Flow Diagram](https://reader031.fdocuments.us/reader031/viewer/2022032114/55a6962d1a28ab6b2d8b45ab/html5/thumbnails/1.jpg)
System Analysis & DesignSystem Analysis & Design
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Where do they fit in?
Analysis (What do we do?) Fact finding
investigate business process and the current system
modelling the current and required systems
deliverables - requirements specification logical models of the
required system
Life Cycle Phases Planning Feasibility Study Analysis Design Code and Unit test
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3
DFDs describe the flow of data or information into and out of a system what does the system do to the data?
A DFD is a graphic representation of the flow of data or information through a system
Data Flow Diagrams (DFD)
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external entity - people or organisations that
send data into the system or receive data from the system
process - models what happens to the data i.e. transforms incoming data into outgoing data
data store - represents permanent data that is used by the system
data flow - models the actual flow of the data between the other elements
4 Main Elements
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Notation
Process box
D Data Store
ExternalEntity
Data Flow
• Data Flow
• Process
• External Entity
• Data Store
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DFD Shapes from Version
F r o m F l o w C h a r t /D a t a F l o w D i a g r a m
P r o c e s s
D a t a S t o r e
E x t e r n a l E n t i t y
F r o m S o f t w a r e D i a g r a m /G a n e - S a r s o n D F D
P r o c e s s
I D #
I D#
E x t e r n a lE n t i t y
D a t a S t o r e1
External Entity
Data Store
Process
From Flow Chart /Data Flow Diagram
Version 5.x Version 2000
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4
Even a small system could have many processes and data flows and DFD could be large and messy use levelled DFDs - view system at different levels of
detail one overview and many progressively greater detailed
views
Levelled DFDs
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models system as one process box which represents
scope of the system identifies external entities and related inputs and
outputs Additional notation - system box
Level 0 - Context Diagram
System boxExternalentity
Data flow out
Data flow in
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gives overview of full system identifies major processes and data flows between
them identifies data stores that are used by the major
processes boundary of level 1 is the context diagram
Level 1 - overview diagram
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level 1 process is expanded into more detail each process in level 1 is decomposed to show its
constituent processes boundary of level 2 is the level 1 process
Level 2 - detailed diagram
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Duplicates marked by diagonal line in corner System Boundary Elementary Processes - star in corner Process that is levelled - dots on top
Other Notation
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5
Numbering Labelling Balancing
Rules for DFDs
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On level 1 processes are numbered 1,2,3… On level 2 processes are numbered x.1, x.2, x.3…
where x is the number of the parent level 1 process Number is used to uniquely identify process not to
represent any order of processing Data store numbers usually D1, D2, D3...
Numbering
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Process label - short description of what the process
does, e.G. Price order Data flow label - noun representing the data flowing
through it e.G. Customer payment Data store label - describes the type of data stored Make labels as meaningful as possible
Labelling
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Balancing
any data flows entering or leaving a parent level must by equivalent to those on the child level
Data stores data stores that are local to a process need not be
included until the process is expanded
Balancing and data stores
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Allowed to combine several data flows from lower
level diagrams at a higher level under one data flow to reduce clutter
Flows should be labelled except when data to or from a data store consists of all items in the data store
Data Flows
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Find the people who send data into the system
Often data is part of a PHYSICAL transaction When handing a bar of chocolate to a shopkeeper, you
are handing him/her a barcode.
Find the people who get data out of the system. The only data you need is data that is transformed or
sent completely out of the system – not data that is handled by an operator within the system.
Context Diagram
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Design StrategyContext Diagram
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Design Strategy
DFD
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Design Strategy
DFD
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Design Strategy
DFD
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Design Strategy
DFD
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