Transcript chap3 seq13.ppt

System Analysis and Design
System Analysis
- Mr. Ahmad Al-Ghoul
Learning Objectives
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Understand the purpose and goals
of producing process description
Discuss and understand the
modular design
Use structured English to analyze
and describe processes
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Process Description Tools
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A process description or
specification
documents the details of a
functional primitive, which
represents a specific set of
processing steps and business logic
Process description link the
process to the DFD and the data
dictionary.
Process description can be
represented in a variety of tools,
the most popular are:
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Structured English
Decision Tables
Decision Trees
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Process Description Tools
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The goals of producing process description are
 Reduce process ambiguity
 Obtain a precise description of what is
accomplished
 Validate the system design, including data
flow diagrams and the data dictionary
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Process Description Tools
Process specifications are not created for:
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Physical input and/or output processes, such
as read and write.
Processes that represent simple data
validation.
Processes for which prewritten code. These
processes are generally included in a system
as subprograms and functions.
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Process Description Tools
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Modular Design
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Based on combinations of three logical structures,
sometimes called control structures which serve as
building blocks for the process
Each logical structure must have a single entry and
exit point
In modular design a rectangle represents a step or
process, diamond shape represents lines in the
direction indicated by the arrows
Three structures
1.
2.
3.
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Sequence
Selection
Iteration - looping
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Process Description Tools
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Modular Design
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Sequence
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The completion of steps in sequential order, one
after anther
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Process Description Tools
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Modular Design
 Selection
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describe a series of alternative policies from which only one
is selected. Represented by
IF
<condition>
<statement>
ELSE
CASE
WHEN <condition> <statements>
WHEN <condition> <statements>
<statement>
…
………..
…...
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Process Description Tools
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Modular Design
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Iteration – looping
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A policy or series of actions is repeated until a
specific condition changes. Represented by
DO…WHILE construct or a REPEAT … UNTIL
construct
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Process Description Tools
Structured English
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Structured English is based on structured logic and Simple English
statements
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Modified form of English used to specify the logic of information
processes
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Uses a subset of English
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Action verbs
Noun phrases
No adjectives or adverbs
No specific standards, Standards vary between organisations
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Must conform to the following rules
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Use only the three building blocks of sequence, selection, and iteration
Use indentation for readability
Use a limited vocabulary, including standard terms used in the data
dictionary and specific words that describe the processing rules
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Process Description Tools
Structured English Example
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The VERIFY ORDER
process description
includes logical rules
and a structured
English version of
the policy. Notice the
alignment and
indentation of the
logic statements.
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Process Description Tools
Structured English Example
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Sample of a policy with logical rules, and a structured English
version of the policy. Notice the alignment and indentation of the
logic statements.
[1]
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Process Description Tools
Data Dictionary and Structured English
The data dictionary is a starting point for
creating structured English:
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Sequenced data dictionary entries become
simple structured English statements.
Selection [] entries become IF..THEN...ELSE
statements.
Iteration { } entries become DO WHILE, DO
UNTIL, or PERFORM UNTIL structured English
statements.
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Process Description Tools
Structured English
Advantages:
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consice and precise, allow easy reading without
ambiguity & misunderstanding
language notation may be tailored to suit user
must exist a cross-referencing with any DFD & DD
entries thus perimitting thourough verification
Disadvantages:
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formality may be alien when first read or write
Avoid assuming that anything written in SE is correct
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Sequence Summary
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Modular Design based on combinations of
three logical structures, sometimes called
control structures which serve as building
blocks for the process
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Three structures, sequence, selection, and
iteration – looping
Structured English uses a subset of
standard English that defines each process
with combinations of the basic building
blocks of sequence, selection, and
iteration
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Sequence Summary
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In this Sequence we have
 Explained the modular design and its three
logical structures, sometimes called control
structures which serve as building blocks for
the process
 Defined and described the three structures,
sequence, selection, and iteration – looping
 Explained how to use structured English to
analyze and describe processes
 Explained the advantages and disadvantages
foe structured English
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Reference
[1] System Analysis and Design, Sixth Edition
Authors: Gary B. Shelly, Thomas J. Cashman and Harry J. Rosenblatt ,
Publisher: SHELLY CASHMAN SEWIES.
[2] system analysis and design, sixth edition
Authors: Kenneth E. Kendall and Julie E. Kendall
Publisher: Prentice Hall
[3] Modern Systems Analysis and Design Third Edition
Authors: Jeffrey A. Hoffer , Joey F. George, Joseph S. Valacich
Publisher: prentice hall
[4] System Analysis and Design, 3rd Edition
Authors: Dennis, Wixom, & Roth
Publisher: John Wiley & sons
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