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Chapter 5: data and process modelling (Data Flow Diagram(DFD) (Process…
Chapter 5: data and process modelling
Data Dictionary
defines and describe all data elements and meaningful combinations of data elements
Also called data item of fiield
uses to collect,document and organize specific facts about system
central store house of information about the system's data
Using Case tools for documentaion
ensure data consistency
more comples the system,more difficult it is to maintain full and accurate documentation
Data Flow Diagram(DFD)
Data flow diagram shows how data move through an information system
Not show program logic or processing step
Process symbol
receives input and produces output that has different content
contain bussiness rules
referred to as a block box
Data Store Symbol
represent data that store in system
Entity Symbol
As a terminator
As a terminator
name of the entity appears inside the symbol
Documenting The Data Elements
attributes usually are recorded and describe
Alias
type and lenght
Data Element And Name
Default value
Acceptable Values
source
security,responsible user and description and comment
Characteristic of data store are
Data store name or label
Description
Alternate name(s)
Attributes
Volume and frequency
Characteristic of process
process Number
process description
Description
Process name and label
Characteristic entity include:
Description
Alternet name
Entitiy name
input data flow
output data flow
Characteristic of a record include:
Definition or description
alternate name(s)
Record or data structure name
attributes
Process Description Tools
modular design
based on combination of three logical stuctures,sometimes called control structure
Sequence
iteration-looping
Selection
Structured English
uses indentation for readability
uses a limited vocabulary
use only three building block of sequence,selection and iteration
Decision Table
the number of rules double each time you add a condition
can have two or more posible outcomes
show a logical structure with all posible combination of conditions and resulting actions
best way to describe a complex set of conditions
Decision trees
Example
Step in creating a set of DFDs
Step 2
: Draw a diagram 0 DFD
if same data flow in both direction you can use double-headed arrow
Diagram 0 is an exploded view of process 0
Step 3
: Draw The lower-Level Diagrams
levelling Example
uses a series of increasingly detail DFDs to describe an infor mation system
such as exploding,partitioning or decomposing
Balancing Example
makesure input and output Parent DFD are maintaned on the child DFD
must use leveling and balancing techniques
Step 1
:Draw a context Diagram
