Some Questions

In PHP 5, what is the difference between using self and $this?

Use $this to refer to the current object. Use self to refer to the current class. In other words, use $this->member for non-static members, use self::$member for static members.

What is Class and Object ?

A class, for example, is like a blueprint for a car. It defines the shape of the car on paper, with relationships between the different parts of the car clearly defined and planned out, even though the car doesn't exist yet .

An object, then, is like the actual Car built according to that blueprint. The data stored in the object is like the gear, wires, and metal that compose the car: without being assembled according to the blueprint, it's just a pile of stuff. However, when it all comes together, it becomes an organized, useful car in running condition .

What is difference Between SOAP and REST 

Read here in detailed answer