Introduction To System Analysis and Design

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.

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

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.

System Analysis vs. System Design Investigation of the problem and requirement rather than solution. System Design: A conceptual solution that fulfills the requirements, rather than implementation.

System Analyst A business professional who uses analysis and design techniques to solve business problems using information technology.

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.

Traditional System Development Life Cycle (SDLC)

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

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

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

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

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.

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).

UML diagrams Can be categorized as the fallowing: Structural diagrams: to show the building blocks of your system—features that don’t change with time. Ex: Class diagram Behavioral diagrams: to show how your system responds to requests or otherwise evolves over time. Ex: Use case diagram 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

UML Diagrams Another way of categorizing UML diagram: Static diagrams to show the static features of the system. (no change) Dynamic diagrams to show how your system evolves over time. Functional diagrams: to show the details of behaviors and algorithms.

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

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

Class Diagram Created During OO Analysis

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

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.

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)

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

Why Objects? Encapsulation Message-based Invocation Data Hiding 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

Classes A 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

Why Class Inheritance Polymorphism a form of reuse means same operation may behave differently on different classes.

Inheritance Example