context process0. student data flow diagram progression
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context
context
Process0
student
student
student
Data Flow Data Flow Diagram Diagram
ProgressioProgressionn
Logical and physical DFDs
Models may focus on either:Models may focus on either:
The “physical” view of the real world –The “physical” view of the real world – howhow things are donethings are done
OROR The “logical” view of the real world – The “logical” view of the real world –
whatwhat things are done things are done
Logical Data Flow Diagrams Logical Data Flow Diagrams AdvantagesAdvantages
Advantages of logical DFDs are:Advantages of logical DFDs are: Better communication with users.Better communication with users. Increased understanding of the business Increased understanding of the business
by analysts.by analysts. The system will have increased The system will have increased
flexibility and be easier to maintain.flexibility and be easier to maintain. Elimination of redundancy.Elimination of redundancy.
Physical Data Flow Physical Data Flow DiagramsDiagrams
Physical data flow diagrams show how the Physical data flow diagrams show how the system operates or how the new system system operates or how the new system will be implemented.will be implemented.
Physical data flow diagrams include:Physical data flow diagrams include: Clarifying which processes are manual and Clarifying which processes are manual and
which are automated.which are automated. Describing processes in greater detail.Describing processes in greater detail. Sequencing processes in the order they must Sequencing processes in the order they must
be executed.be executed.
Physical Data Flow Physical Data Flow DiagramsDiagrams
Physical data flow diagrams include Physical data flow diagrams include (continued):(continued): Temporary data stores and transaction files.Temporary data stores and transaction files. Specifying actual document and file names.Specifying actual document and file names. Data flows and data stores are labeled with Data flows and data stores are labeled with
the actual name of the physical media on the actual name of the physical media on which data flow or in which data are storedwhich data flow or in which data are stored
Controls to ensure accuracy and Controls to ensure accuracy and completeness.completeness.
Customer Order
Valid salesordersCheck
Salesorders
Sales orders
reject
Logical and Physical DFDsPhysical DFDs Logical DFDs
View How processing is implemented
What the system does
Processes Actual sequence Essential sequence
Naming Forms, locations, people/roles
Underlying data and activities
Data flows Detailed/ specific/ duplicated data describing exact
Only essential inputs and outputs of the
processes implementation needs
Process modeling
Principal techniques Data flow diagrams Function decomposition
function decomposition diagrams showing only higher levels can be built early in systems analysis
Function Decomposition Function decomposition is the decomposing of a
system into its component functions and processes as a way of managing complexity
Function decomposition creates a top-down view: it shows a hierarchy of levels of increasingly detailed processes within a system
the decomposition of functions corresponds to leveling of processes in DFDs
this structure may not correspond to the structure of the organization shown in an organization chart
Function Decomposition They may be built using either a top
down or a bottom up approach
They provide a useful overview of the processing within a system