System analysis and design chapter 7 Data flow diagram What\'s the difference am
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Question
System analysis and design chapter 7 Data flow diagramWhat's the difference among the four levels of DFD: current physical, current logical, New physical, and new logical. What's the difference in each of these levels as well as what occurs at each of these levels each day System analysis and design chapter 7 Data flow diagram
What's the difference among the four levels of DFD: current physical, current logical, New physical, and new logical. What's the difference in each of these levels as well as what occurs at each of these levels each day System analysis and design chapter 7 Data flow diagram
Explanation / Answer
Process Modeling and Data Flow Diagrams (DFD) Graphically representing the functions, or processes, which capture, manipulate, store, and distribute data between a system and its environment and between components of a system
Data Flow Diagram (DFD) graphical representation of data processes and flows throughout the organization emphasizes logic of underlying system
Based on general systems model
Input -----> process---> output
Why Use DFD? Logical information flow of the system determination of physical system construction requirements simplicity of notation establishment of manual and automated systems requirements
Advantages of DFD-->Early understanding of system technical implications Establishment of inter-relatedness between business and systems user involvement with system development determine if data and processes have been defined properly
Four Different Types of DFDs
Current Physical
Process labels identify technology (people or systems) used to process the data.
Data flows and data stores identify actual name of the physical media.
Current Logical
Physical aspects of system are removed as much as possible.
Current system is reduced to data and processes that transform them.
New Logical
Includes additional functions.
Obsolete functions are removed.
Inefficient data flows are reorganized.
New Physical
Represents the physical implementation of the new system.
Physical vs. Logical
Guidelines for Drawing DFDs
Completeness DFD must include all components necessary for system.
Each component must be fully described in the project dictionary or CASE repository.
Consistency--The extent to which information contained on one level of a set of nested DFDs is also included on other levels.
Timing----Time is not represented well on DFDs.Best to draw DFDs as if the system has never started and will never stop.
Iterative Development--Analyst should expect to redraw diagram several times before reaching the closest approximation to the system being modeled.
Primitive DFDs---Lowest logical level of decomposition.Decision has to be made when to stop decomposition
Logical DFD - Advantages --Better communication,More stable systems,Better understanding,Flexibility and maintenance,Elimination of redundancies
Physical DFD - Advantages----Clarifying manual & automated processes,Detailed process description,Sequencing processes,Identifying temporary data stores,Specifying name of files and printouts,Adding control
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