Object modeling

Object and Classes- 

• Class- A template or blueprint that defines the characteristics of an object and describes how the object should look and behave.
•  Object- Object is an instance of a class. Combining both data and member functions. Objects are the basic run-time entities in an objectoriented system.

Links and Association-

•  Association is a relationship between two objects. In other words, association defines the multiplicity between objects.
•  When the association is between two classes, its called Binary Association. When the association is between two instances of the same class, then its called reflexive or unary association.
•  Example : Binary Association : Employee works for Employee Unary Association: A Employee supervises Employees

        Link-Link is the relationship between two objects. There are no multiplicity concepts in links. Links always exists between two objects.

Generalization And Inheritance-

Generalization-

• Generalization is the process of extracting shared characteristics from two or more classes, and combining them into a generalized superclass.

Inheritance-

• Inheritance in Object Oriented Programming can be described as a process of creating new classes from existing classes. New classes inherit some of the properties and behavior of the existing classes.

Aggregation-

• Aggregation is a way of composing different abstractions together in defining a class. For example, a car class can be defined to contain other classes such as engine class, seat class, wheels class etc.

Abstract Class-

• Multiple inheritance is a feature of some object-oriented computer programming languages in which an object or class can inheritcharacteristics and features from more than one parent object or parent class.

Meta Data-

• Metadata is data that describes other data. Meta is a prefix that in most information technology usages means "an underlying definition or description."  Metadata is data that describes other data. Meta is a prefix that in most information technology usages means "an underlying definition or description."

Candidate Key-

A candidate key is a column, or set of columns, in a table that can uniquely identify any database record without referring to any other data. Each table may have one or more candidate keys, but one candidate key is unique, and it is called the primary key.

Constraints-

A constraint is a packageable element which represents some condition, restriction or assertion related to some element (that owns the constraint) or several elements. Constraint is usually specified by a Boolean expression which must evaluate to a true or false.