Abstract Class
An abstract class is a class that is only partially implemented by the programmer. It may contain one or more abstract methods. An abstract method is simply a function definition that serves to tell the programmer that the method must be implemented in a child class.
Interface
An interface is similar to an abstract class; indeed interfaces occupy the same namespace as classes and abstract classes. For that reason, you cannot define an interface with the same name as a class. An interface is a fully abstract class; none of its methods are implemented and instead of a class sub-classing from it, it is said to implement that interface.
An interface will be used in the database abstraction layer you create. This ensures that every time you create a class for a particular database, the same API is exposed. When using an interface, you can then rely on the methods defined for the interface to be part of the class because, if they are not, PHP will not parse it.
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