Object-Oriented Analysis and Design (OOAD)

• Module 1 introduces Object-Oriented Analysis and Design (OOAD).

Objectives

• Understand the rationale behind object-oriented approaches.
• Define what OOAD is and its core concepts.
• Learn how to apply OOAD in software development.

Why Object-Oriented?

• Software crises arose from communication difficulties and complexity management in software development.
• The Whorfian Hypothesis states that language shapes our understanding and organization of the world.
• Object-oriented languages alleviate communication & complexity difficulties.

OOAD Defined

• OOAD is a software engineering methodology using object-oriented concepts for system analysis and design.
• OOAD organizes complex software systems.
• OOAD facilitates reusability and maintainability.
• OOAD ensures clear communication among stakeholders.

Phases of OOAD

• Object-Oriented Analysis (OOA) focuses on identifying system objects and understanding requirements.
• Object-Oriented Design (OOD) translates the analysis model into a design by defining classes, methods, and interactions.
• Implementation involves coding the system based on the design.
• Testing and Maintenance validates and maintains the system.

Key Concepts in OOAD

• Objects are entities with state, behavior, and identity.
• Classes are templates for objects, defining their state and behavior.
• Encapsulation hides object data and provides managed access via methods.
• Inheritance reuses code through class hierarchies.
• Polymorphism enables objects to respond differently to the same message.
• Abstraction hides complex details, showing only essential features.

Object-Oriented Analysis (OOA)

• The objective of OOA is to identify the system's main objects, interactions, and relationships.
• Identify Objects to recognize key entities in the system.
• Define Relationships to specify how objects interact.
• Define Behavior to specify actions and messages for objects.
• The outcome is a clear understanding of system requirements and object behavior.

Object-Oriented Design (OOD)

• The objective of OOD is to convert analysis models into executable code.
• Design Classes to define classes and their attributes.
• Design Methods to define methods and interactions.
• Design Interfaces to specify how different components interact.
• The outcome is a detailed design that can be implemented into code.

Benefits of OOAD

• Modularity allows easier breakdown of systems into reusable modules.
• Reusability encourages code reuse through inheritance and polymorphism.
• Maintainability makes objects easier to maintain and update.
• Scalability ensures systems can be easily scaled or enhanced.

Object-Oriented Modeling

• UML (Unified Modeling Language) is a standard modeling language for OOAD.
• Use Case Diagram represents system functionality from the user's perspective.
• Class Diagram represents the structure of the system and its relationships.
• Sequence Diagram shows interactions between objects over time.
• State Diagram represents the states of an object and its transitions.

OOAD vs Traditional Design Approaches

• Traditional Design often uses a data-centric approach where systems are designed based on databases and data flow.
• OOAD focuses on real-world objects and their interactions.
• OOAD is object-based and more adaptable to changes in business requirements.

Why Object-Oriented? Human Growth & Concept Formation

• Communication and complexity are expressed through concepts in a language.
• Human growth and concept formation are considered when using an object-oriented language.
• The world appears as a buzzing confusion to infants.
• "Blue sky" is an individual concept to a very young age child.
• The world is explained through conceptual constructs as we get older.
• Language is used to create concept diagrams.
• Models serve as a simplification of reality and as an abstraction for understanding.

What is Object-Orientation?

• An "object" applies to a concept based on our awareness.
• Objects are drawn from the problem domain or solution space.
• Object-orientation is the structure that has identity, properties, and behavior.
• Object-orientation is an instance of a collective concept - a class.
• Abstraction focuses on the essential and omits details.
• Encapsulation is information hiding where objects encapsulate property, behavior, and state.
• Classes share common properties, attributes, behavior, and semantics.

Object-Orientation: Subclass vs. Superclass

• Specialization defines one class as refinement of another.
• A subclass is defined in terms of a specialization of a superclass using inheritance.
• A superclass serves as a base for inheritance in a class hierarchy.
• Inheritance is automatic duplication of superclass attribute and behavior definitions in subclass.

Polymorphism

• Polymorphism exists when objects of different classes respond to the same message differently.

Object-Orientation: Interfaces

• Grade information should be kept private to the student, and accessed through interfaces.
• Information hiding means all data should be hidden within a class.
• Data attributes should be made private.
• Public methods get and set data values.

Object-Orientation: Abstract Class vs Concrete Class

• An abstract class is an incomplete superclass that defines common parts and cannot be instantiated.
• A concrete class is a complete, fully described concept that is intended to be instantiated.

Object-Orientation: State

• "State" is a collection of associations an object has with other objects and object types.
• A "state change" is the transition of an object from one state to another.
• An "event" is a noteworthy change in state.

Object-Oriented Application

• A collection of discrete objects, interacting with each other is an Object-Oriented Application.
• Objects have property and behavior (causing state transition).
• Interactions occur through message passing.

What is OOAD?

• Analysis involves understanding, finding, and describing concepts in the problem domain.
• Design involves understanding and defining software solutions/objects that represent the analysis concepts.
• OOAD involves both a notation and a process.

Summary of Key Points

• A software crisis occurred due to communication and complexity issues.
• Object-oriented languages, concepts, and models must be employed for conceptual modeling.
• Fundamental OO Concepts and a little taste of UML are helpful.
• OO development processes and Design Patterns can be used.