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DFD Basics
- Graphical representation of the flow of data throughout a system
- shows what kinds of information will be input to and output from the system
- Also shows where data will come from and go to, and where the data will be stored
- Also shows where data will come from and go to, and where the data will be stored
- does not show information about the timing, or about whether
processes will operate in sequence or in parallel
- common practice to draw the context-level data flow diagram first
- shows the interaction between the system and external agents which act as data sources
- context diagram shows the entire system as a single process, and
gives no clues as to its internal organization
- context diagram shows the entire system as a single process, and
gives no clues as to its internal organization
- Context Level DFD
- no inside workings of the
process are detailed
- no inside workings of the
process are detailed
- shows the interaction between the system and external agents which act as data sources
- Level 1 DFD that shows some of the detail of the
system being modeled
- shows how the system is divided into sub-systems
(processes)
- Every process detailed on the level 0 diagram
has a level 1 diagram
- Must be balanced - i.e. show same input/output flows & data
stores as detailed in level 0 DFD
- Must be balanced - i.e. show same input/output flows & data
stores as detailed in level 0 DFD
- Every process detailed on the level 0 diagram
has a level 1 diagram
- shows how the system is divided into sub-systems
(processes)
- Data flow diagrams can be used in both Analysis and Design phase of SDLC.
- Gane and Sarson Elements
- Process - has a number, name,
description, at least one output flow, at
least one input flow
- Data flow arrow - has a name, one or more
connections to a process
- Data store - has a number, name, description, 1 or more output
flows, 1 or more input flows
- External entity - has a name and
description
- Process - has a number, name,
description, at least one output flow, at
least one input flow
- Level 0 DFD
- Shows all processes, data stores,external
entities, and data flows amongst them
- Purpose is to show major high level
processes that are interrelated
- Overview of the system
- Shows all processes, data stores,external
entities, and data flows amongst them
- Level 2 DFD
- Shows a level 1 DFD in more detail
- Again has to be balanced by showing the same
input/output flows & data stores as the level 1
equivalent
- Numbering at this level
has two decimal points
e.g. 1.2.4
- Shows a level 1 DFD in more detail
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