Object-Oriented Modeling and Design

It is a new way of thinking about problems using models based on real world concepts. The basic construct is object which combines both data structure and behaviour in a single entity. The Object Modelling Technique (OMT) which extends from analysis through design to implementation.

• Analysis model is built to abstract essential aspects of application domain which contains objects found in application, their properties and behaviour.
• Then design model is made to describe and optimise the implementation.
• Finally the design model is implemented in a programming language, database or hardware.
• Graphical notation is used for expressing object-oriented models.

What is object-oriented?

• Software is organised as a collection of discrete objects that incorporate both data structure and behaviour.
• In general it includes- identity, classification, polymorphism and inheritance.
• Object Oriented Programming Language = Object Based Programming Language(e.g. '83 Ada and Modula-2)+ Inheritance + Dynamic Binding

Identity

• Identity means that data is organized into discrete, distinguishable entities called objects.
• Objects can be concrete or conceptual.
• In real world an object simply exist but within a programming language each object has a unique handle by which it can be uniquely referenced.
• The handle can be implemented by address, array index or unique value of an attribute.

Classification

• It means that objects with same data structure (attribute) and behavior (operations) are grouped into a class.
• A class is an abstraction that describes important properties and ignores the rest.

Polymorphism

• It means that the same operation (i.e. action or transformation that the object performs) may behave differently on different classes.
• Specific implementation of an operation by a certain class is called a method.

Inheritance

• It is the sharing of attributes and operations among classes based on a hierarchical relationship.
• Subclasses can be formed from broadly defined class.
• Each subclass incorporates or inherits all the properties of its super class and adds its own unique properties.

Object-Oriented Development?

• The theme is the identification and organisation of application concepts rather than final representation in a programming Language.
• OOD approach encourages software developers to work and think in terms of the application domain through most of the software engineering life cycle.
• It is a conceptual process independent of a programming language until the final stage.

1. Analysis
2. System design
3. Object design
4. implementation

Object model

• Describes basic structure of objects and their relationship
• Contains object diagram
• Object diagram is a graph whose nodes are object classes (Classes) and whose arcs are relationships among classes.

Dynamic model

• Describes the aspects of a system that change over time.
• It specifies and implement control aspects of a system.
• Contains state diagram.
• State diagram is a graph whose nodes are states and whose arcs are data-flows.

Functional Model

• Describes data value transformation within a system.
• Contains data flow diagram.
• Data Flow Diagram is a graph whose nodes are processes and whose arcs are data flows.

Object-Oriented Concepts

• Abstraction
• Encapsulation
• Combining data and behaviour
• Sharing
• Object structure, not Procedure Structure
• Synergy