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Introduction To System Analysis and Design

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What Is An Information System? An information system is a collection of

interrelated components that collect, process, store, and provide as output the information needed to complete a business task.

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Examples of Information Systems Course registration system Online order system Online banking system

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What Is System Analysis About? Understanding the goals and strategies of the

business. Defining the information requirements that

support those goals and strategies. It is not about programming.

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System Analysis vs. System Design System Analysis:

Investigation of the problem and requirement rather than solution.

System Design: A conceptual solution that fulfills the

requirements, rather than implementation.

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System Analyst A business professional who uses analysis and

design techniques to solve business problems using information technology.

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The Role of a System Analyst Investigate, analyze, design, develop, install,

evaluate, and maintain a company’s information systems.

Business knowledge. Business problem solver. Help translate business requirements into IT

projects.

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Traditional System Development Life Cycle (SDLC)

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Traditional System Development life Cycle (SDLC) Project planning – initiate, ensure

feasibility, plan schedule, obtain approval for project

Analysis – understand business needs and processing requirements

Design – define solution system based on requirements and analysis decisions

Implementation – construct, test, train users, and install new system

Support – keep system running and improve it

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Two Approaches to System Development Traditional (Structured) approach

Also called structured system development Structured analysis and design technique

(SADT) Includes information engineering (IE)

Object-oriented approach Also called OOA, OOD, and OOP Views information system as collection of

interacting objects that work together to accomplish tasks

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Structured System Development Structure Programming Top-down Programming Structured Design Structured Analysis

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Object-Oriented Approach Completely different approach to

information systems Views information system as collection of

interacting objects that work together to accomplish tasks Objects – things in computer system that can

respond to messages Conceptually, no processes, programs, data

entities, or files are defined – just objects OO languages: Java, C++, C# .NET,

VB .NET

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Object-oriented Analysis and design (OOAD)

OOAD essential for creating well-designed, & maintainable software system All Software Analysis and Design is preceded

by the analysis of requirements. Analysis models the “real-world”

requirements, independent of the implementation environment.

Design applies object-oriented concepts to develop and communicate the architecture and details of how to meet requirements.

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Unified Modeling Language (UML) UML (Unified Modeling Language) is a graphical

language that is suit-able to express software or system requirements, architecture, and design.

UML used for both database and software modeling

UML modeling also supports multiple views of the same system. use case diagram shows the purposes of the system

(use cases) and the users (actors).

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UML diagrams Can be categorized as the fallowing:

1. Structural diagrams: to show the building blocks of your system—features that don’t

change with time. Ex: Class diagram

2. Behavioral diagrams: to show how your system responds to requests or otherwise evolves

over time. Ex: Use case diagram

3. Interaction diagrams: Is a type of behavioral diagram. To depict the exchange of messages within a collaboration (a group of

cooperating objects). Ex: Sequence diagram & Collaboration diagram

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UML Diagrams

Another way of categorizing UML diagram:

1. Static diagrams to show the static features of the system. (no

change)

2. Dynamic diagrams• to show how your system evolves over time.

3. Functional diagrams: • to show the details of behaviors and algorithms.

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Object-oriented analysis (OOA) Trying to figure out what the users and customers

of a software effort want the System to do. Builds a “real-world” model from requirements

client interviews, domain knowledge, real-world experience collected in use cases and other simple notations

OOA models address three aspects of the system (its objects) class structure and relationships sequencing of interactions and events data transformations and computations

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Models of Object-Oriented Analysis (UML)

Structural Model (Data-Oriented) static features what objects are in the system? how are they related?

Dynamic Model (Action-Oriented) behavioral aspects what events occur in the system when do they occur and in what order?

Functional Model (Both Data and Actions) data transformations “what” does the system do

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Class Diagram Created During OO Analysis

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Ex: Use Case (Analysis)

Start from requirements Describe response of system to events

– Normal flow of action– Error and exception handling

Can implement tests to check use cases

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OOD: Object Oriented Design

• Emphasizes a conceptual solution that fulfils the

requirements specified in the analysis.

• Need to define software objects and how they

collaborate to fulfill the requirements.

• For example, in the Library Information System, a

Book object may have a title attribute and a

display() method.

• Designs are implemented in a programming

language.

•In the example, we will have a Book class in Java.

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Objects In an OO approach, a system consist of a collection

of interacting objects. An object is a computational entity which Provide

services with which other entities may interact ○Typically, the services consumer sends a

message ( requesting the service) to the provides object ○Possesses

Sate -Information that the object holds , called (attributes)

Behaviour -Operation it can perform , called (method)

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Messages Interaction is achieved by one object sending

a message to another Message has

A sender A receiver Message contents :

A reference to an operation of the receiver Possible additional information (parameters)

Some messages return information to the sender

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Why Objects? Encapsulation

Helps to organize data & behavior into meaningful associations.

Message-based Invocation Helps to make code adaptable and reusable

Data Hiding Helps to manage complexity, since programmer

can control the data that objects are allowed to do manipulate

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ClassesA Class Describes a set of equivalent objects

○Hence, operates like a data type of objects ○Typically, every object in a system belongs to a

class Provides a useful way of representing and

implementing the shared state and behavior of the objects that it describes

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Why Class

Inheritance a form of reuse

Polymorphism means same operation may behave differently on

different classes.

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Inheritance Example