Let’s consider a simple sample:
Contact db table: Contact ID (primary key), Contact Name, Contact Address
Employee db table: Employee ID (primary key), Employee Joining Date
Customer db table: Customer ID (primary key), Customer Birth Date
Now to utilize the object oriented inheritance concept in relational database model, we can create a one to one relation with Contact table with Employee and Customer table, where besides primary key, Employee ID and Customer ID will be used as the foreign key of Contact table, regarding the concept that all Employees and Customers are considered as a “Contact” object.
Now if we wish to map this idea to real world OOP code, we will create a business entity named “Contact” which inherited sub classes will be “Employee” and “Customer” business entity. The corresponding BLL and/or DAL (Data Access Layer) class of “Employee” or “Customer” can also be inherited from BLL (Business Logic Layer) and/or DAL class of “Contact” to perform required operations in object oriented manner.