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3.2 DATA & PROCESS MODELLING - Coggle Diagram
3.2 DATA & PROCESS MODELLING
Data & Process Modelling Concepts
A data flow diagram (DFD) uses various symbols to show how the system transforms input data into useful information.
Data Flow Diagram
shows how data moves through an information system but does not show program logic or processing steps
provides a logical model that shows what the system does, not how it does it
DFD Symbols
Process symbol
Receives input data and produces output that has a different content, form, or both
Referred to as a black box
Data flow symbol
Represents one or more data items
symbol for a data flow is a line with a single or double arrowhead
Data store symbo
l
Represent data that the system stores
Entity Symbol
Name of the entity appears inside the symbol
Shows only external entities that provide data to the system or receive output from the system
.
Creating a set of DFD
Step 1 : Draw a context diagram
Step 2: Draw a Diagram 0 DFD
Step 3: Draw the Lower-Level Diagrams
Leveling example :
Leveling uses a series of increasingly detailed DFDs to describe an information system.
is called exploding, partitioning, or decomposing.
Balancing example
Ensures that the input and output data flows of the parent DFD are maintained on the child DFD
Data Dictionary
is a central storehouse of information about the system’s data
Documenting the Data Elements
Data Flows
Processes
Data Elements
Data Stores
Entities
Records
Process Description (3)
Modular design
based on combinations of three logical structures, sometimes called control structures, which serve as building blocks for the process.
three structures
sequence
selection
iteration
Structured English
Use a limited vocabulary, including standard terms used in the data dictionary and specific words that describe the processing rules
Decision Table
Shows a logical structure, with all possible combinations of conditions and resulting actions
