Object oriented programming (OOP) was first introduced in php4. Area for oop in php version 4 was not very vast. There were only few features available in php4. Major concept of the object oriented programming in PHP is introduced from version 5(we commonly known as php5). Also php community has plan to modify its object model structure in more better manner in php6(not released yet). But still in php5 object model is designed nicely. If you have good understanding of OOP then you can create very good architecture of your php application. You only need to know some of the basic principles of object oriented programming and how to implement that concept of oop in php. In whole series I will use abbreviation OOP for Object Oriented Programming.