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Data Flow Diagram Progression

Logical and physical DFDs Models may focus on either: Models may focus on either: The “ physical ” view of the real world – how things are done The “ physical ” view of the real world – how things are doneOR The “ logical ” view of the real world – what things are done The “ logical ” view of the real world – what things are done

Logical Data Flow Diagrams Advantages Advantages of logical DFDs are: Advantages of logical DFDs are: Better communication with users. Better communication with users. Increased understanding of the business by analysts. Increased understanding of the business by analysts. The system will have increased flexibility and be easier to maintain. The system will have increased flexibility and be easier to maintain. Elimination of redundancy. Elimination of redundancy.

Physical Data Flow Diagrams Physical data flow diagrams show how the system operates or how the new system will be implemented. Physical data flow diagrams show how the system operates or how the new system will be implemented. Physical data flow diagrams include: Physical data flow diagrams include: Clarifying which processes are manual and which are automated. Clarifying which processes are manual and which are automated. Describing processes in greater detail. Describing processes in greater detail. Sequencing processes in the order they must be executed. Sequencing processes in the order they must be executed.

Physical Data Flow Diagrams Physical data flow diagrams include (continued): Physical data flow diagrams include (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 the actual name of the physical media on which data flow or in which data are stored Data flows and data stores are labeled with the actual name of the physical media on which data flow or in which data are stored Controls to ensure accuracy and completeness. Controls to ensure accuracy and completeness.

Customer Order

Valid sales orders Check Sales orders Sales orders reject

Logical and Physical DFDs Logical DFDsPhysical DFDs What the system doesHow processing is implementedView Essential sequenceActual sequenceProcesses Underlying data and activities Forms, locations, people/rolesNaming Only essential inputs and outputs of the Detailed/ specific/ duplicated data describing exact Data flows needsimplementationprocesses

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