BCS414 41

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Chapter 4
Data and Process Modeling

• Structure Analysis
• describes a system in terms of
• Input
• Output
• Data and
• Process

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• Structure Analysis
• involves 3 main tools
• Data Flow Diagrams
• Data Dictionary
• Process Description

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• Data Flow Diagrams DFD
• Shows how data moves through an information
  system
• (what the system does)
• but not show program logic or processing steps
• (not how it does)
• DFD Symbols
• Process Symbol
• Data Flow Symbol
• Data Store Symbol
• External Entity Symbol

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Process Symbol Receives input data and produces
output Data Flow Symbol Path for data to move
from one part of the information systems to
another Data Store Symbol Represent a
situation in which system must retain
data External Entity Symbol Person, department,
outside organization or other information system
that provides data to the system or receives
output from the system
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• Context Diagrams
• Top-level view of an information system that
  shows the systems boundaries and scope
• Conventions for DFD
• Must fit on one page
• Process name should be the name of information
  system
• Use unique names within each set of symbols
• Do not cross lines
• Use unique reference number for each process
  symbol

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Strategies for Developing DFD A set of DFD is a
graphical, top-down model   Create context
diagram, then diagram 0, then all the
child diagram for
diagram 0, and so on
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• Data Dictionary
• Central storehouse of information about
• the systems data
• Define and describe all data elements and
• meaningful combination of data elements

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Data Dictionary
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Documenting the Data Flow
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Documenting the Data Stores
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Documenting the Process
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Documenting the External Entities
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Documenting the Records
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• Process Description Tools
• Modular Design building blocks for the
  process
• combine of 3 logical structures
• 1.    Sequence
• 2.    Selection
• 3.    Iteration
• Structured English
• Decision Tables
• Decision Trees

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Modular Design
Sequence
Selection
Iteration
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Structured English
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Decision Tables
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Decision Trees
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Sequence of models between logical and physical
models? Four-Model Approach 1.    Physical model
of the current system 2.    Logical model of the
current system 3.    Logical model of the new
system 4.    Physical model of the new system
 
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Process ???????????????? Data Store ??????????????
??????? ??????
Entity ???????????????????? ??????????? ?????????
Data Store ?????????? Process ??????