How api concepts comes code example

Example: what is api

API (Application Programming Interface) helps in communication 
and data exchange between two software systems. It is the channel which 
connects two software systems communicate with one another.


An API forms the middle layer of a three-layered application pyramid, 
consisting of a data layer, a server layer and a presentation layer. 
While the data layer is concerned with data storage and the presentation 
layers are concerned with the user interface, the server layer is composed 
of business logic that defines the way for users to interact with various 
functions, features, and information. 

RESTful API ==> plain text, html, xml, json
SOAP ==> more secure, works with only xml