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System Analysis and Design
(Professional Solutions)
Week 1 : Introduction to SAD

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Today’s Activities
• Module overview
• Ice-breaking
• Lecture – Introduction to SAD
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Module Overview
• Module : System Analysis and Design (Professional Solutions)
• Level 4 with 20 Credits
• Lets see Module Descriptor
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Ice breaking
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Content
• Introduction to processes involve in Analysis and Design
• Revise Structured Approach
• Revise Object Oriented Approach
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What Is Systems Analysis and Design
(SAD)?
The process of implementing and operating an
information system
Requires knowledge of:
• Organization’s objectives, structure, processes
• Information technology opportunities and constraints
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What Is Systems Analysis and
Design?
The major goal of SAD is :
“to improve organizational systems, typically by
developing application software/system that can help
employees accomplish key business tasks easily and
efficiently”
A system is designed to support a specific organizational function or
process (inventory management, payroll, etc)
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Analysis
Its meaning (Greek word) “to break down into
component parts”.
It is a process of coming to understand fully the
problem that is trying to be solved.
Analysis activity is characterized as asking:
• What happens in current system?
• What is required in the new system?
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Definitions

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Analysis
It is a process of seeking to:
• Understand the organization
• Investigating its requirement, and
• Modeling them.
Result : A specification of what the proposed system
will do based on requirements (requirement
specification).
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Definitions

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Design
Design activity is concerned with specifying:
• How the new system will meet the requirements?
It is a process of :
• Producing a solution that meets the requirements that have
been analysed.
Jacobson et. al (1992) regards:
“design as a part of construction process (together with
implementation)”
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Definitions

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Analysis Design
Role of Systems
Analyst
Role of Systems
Designer
Description of the Problems Description of the Solutions
Analysis and design can be viewed as follows:
Definitions

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Systems Analysis
 Process of
• defining the problems
• gathering the requirements
• developing an analysis model representing those
requirements
 Describing the problem the system is meant to solve
 Goal:
• To state accurately the users’ requirements for a new
information processing system
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Definitions

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Systems Design
A process by which the analysis model is transformed into a
model which is capable of being implemented
Describing the solution to the problems
Goals:
• Satisfaction of requirements
• Provide effective function
• Performance
• Specify the acceptable level of performance
• Constructability
• Feasible to construct the new system/artifact
• Efficient design process
• Maximizing the efficiency of the process
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Definitions

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Add formality
Improve communication between participants
Get the requirements right!
Reduce errors
The cost of fixing analysis and design errors as one
moves from the analysis phase to the maintenance
phase can increase by a factor of 100
Generate documentation and get approval from
end-user.
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The Purpose of Analysis and Design

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Cost of Analysis and Design Error

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Source: Pressman
Specification/requirements/design: 63.7%
Source of errors

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 Structured Approach made of three
techniques
 Structured analysis
 Structured design techniques
 Structured programming
 Collectively referred to as structured
analysis and design technique (SADT)
Structured Approach

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Structured Analysis
• Helps developer define what the system needs to do (processing
requirements)
• Data to store and use
• Inputs and outputs
• How functions work together
• DFDs and ERDs commonly used to show results of structured analysis
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Structured Approach

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Structured Approach,
Data Flow Diagram (DFD)

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Structured Approach
Entity Relationship Diagram (ERD)

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Structured design is developed to provide guidelines :
•What the set of programs should be?
•What each program should accomplish?
•How programs should be organized into a
hierarchy?
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Structured Approach

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Structured Approach
Structure Chart –using Structured Design
Technique

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Structured Programming
• The process of implementing a structured design
• Developed in the 1960’s to improve computer program quality and allow
other programmers to easily read and modify the code
• Each program module has one beginning and one ending
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Structured Approach

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Views information systems as collections of interacting objects that
work together to accomplish tasks
Objects - a thing in the computer system that can respond to
messages
No processes, programs, data entities, or files
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Object-oriented Approach

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 Object-oriented analysis
• Defines all types of objects that do the work of the
system
• Shows how objects interact
 Object-oriented design
• Defines all additional object types needed to
communicate with people and devices in the system
• Refines each type of object for implementation in a
specific language and environment
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Object-oriented Analysis and Design

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The main concepts introduced here are:
• Objects, Classes and Instances
• Object State
• Generalization and Specialization
• Message-passing and Encapsulation
• Polymorphism
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Based on Chapter 4 of Bennett, McRobb and Farmer:
Object Oriented Systems Analysis and Design Using UML, (2nd
Edition), McGraw Hill, 2002.
What is object orientation

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An object is:
“an abstraction of something in a problem domain,
reflecting the capabilities of the system to”
 keep information about it,
 interact with it,
 or both.
Coad and Yourdon (1990)
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Objects

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“Objects have state, behaviour and identity.”
Booch (1994)
State: the condition of an object at any moment, affecting how it
can behave
Behaviour: what an object can do, how it can respond to events
and stimuli
Identity: each object is unique
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Objects

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Object
A person. ‘Hussain Pervez.’ Speak, walk, read.
Studying, resting,
qualified.
A shirt.
My favourite button
white denim shirt.
Shrink, stain, rip. Pressed, dirty,
worn.
A sale. Sale no #0015,
16/06/02.
Earn loyalty points. Invoiced,
cancelled.
Identity Behaviour State
A bottle of
ketchup.
This bottle of
ketchup.
Spill in transit. Unsold, opened,
empty.
Examples of Objects

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What Is an Object?
An entity that encapsulates data and behavior
Objects are categorized into classes
Each individual object is an instance of a class
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What Is Encapsulation?
The characteristic of object-orientation in which data
and behavior are bundled into a class and hidden from
the outside world
Access to the data and behavior is provided and
controlled through an object’s interface
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Class - a category of objects that share the same:
• attributes,
• operations/methods
• relationships and semantics
All objects are instances of some class
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What Is Class?

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Name
Attributes
Operations

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What Is an Attribute?
Attribute- a named property of a class that describes a
range of values that instances of the attribute might
hold
Attributes are the way classes encapsulate data
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Attributes
are
properties
containing
values
Minus
sign
indicates
these are
private
(hidden)

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What Is an Operation?
A behavior of an object
Implemented in classes are methods
Methods are identified and invoked by their signatures,
including name, parameters, and return type
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Signature identifies
and invokes the
behavior
Method implements the behavior

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Method
signatures
Plus sign
indicates
these are
public
(accessible)

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What Is Generalization?
A relationship between a more general (or parent) class
and a more specific (or child) class
The more specific class has additional attributes and
operations
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What Is Inheritance?
The mechanism by which the more specific class in a
generalization relationship includes the attributes and
operations of the more general class
Actually, inheritance is the facility in an O-O language
that implements generalization/specialization
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Generalization
represented by
arrows from
subclass to super
class
Subclasses
inherit all
attributes and
operations of
super classes

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Person
Employee Customer Supplier
monthly
paid
weekly
paid
hourly
paid
Driver Cleaner Sales
assistant
More general
(superclasses)
More specialized
(subclasses)
Specialization Hierarchy

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What Is Polymorphism?
The ability for different classes of objects to respond to
identical messages in different ways
Polymorphism = “having many forms”
Different behaviors for the same message
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Here, each
type of
vehicle has
its own
version of
calcPrice()

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Can save effort
• Reuse of generalized components cuts work, cost and time
Can improve software quality
• Encapsulation increases modularity
• Sub-systems less coupled to each other
• Better translations between analysis and design models and working code
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Advantages of Object Orientation

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THE WAY WE THINK ABOUT PROBLEMS
OO approach
• Model the world as it is
• Simulation based modelling
Structured approach
• Model the world as a set of functions
• Solution based modelling
The Difference in Philosophy

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THE WAY WE SUB-DIVIDE THE PROBLEM
- encapsulation
- information hiding
- abstraction
OO approach based on:
Can only achieve encapsulation and
information hiding through discipline
Structured approach
The Difference in Philosophy

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THE RELATIONSHIP BETWEEN ANALYSIS
AND DESIGN
• Phases are related by refinement
Classes
has-a
is-a
Classes
has-a
is-a
Refinement
OO approach
The Difference in Philosophy

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THE RELATIONSHIP BETWEEN ANALYSIS
AND DESIGN
• Phases are related by transformation
DFDs
Structure
Charts
Transformation
Structured approach
The Difference in Philosophy

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OO Approach
- consideration of the user interface
• identify Use-cases
• identify classes, attributes, operations and relationships
• identify behaviour
- identification of abstract classes
- identification of data managers
• refine analysis model to a design model by:
- consideration of detailed user requirements
The Difference in Philosophy

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Structured Approach
• build a hierarchy of DFDs
• identify an overall process
• identify external entities
• transform DFDs to structure charts
The Difference in Philosophy

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Conclusion
• Introduction to processes involve in Analysis and Design
• Structured Approach – several modelling techniques –
DFD, ERF, Structures Design technique
• Object Oriented Approach – concepts of object,
encapsulation, polymorphism
• Differences between structured approach and OO
approach
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Resource
• Chapter 3 and 4. Simon Bernett, Steve Mc Robb and Ray Farmer.
Object-oriented System Analysis and Design Using UML.
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