Introduction to REST

REST stands for REpresentational State Transfer, it is a software architecture for building webservices. Usually REST is not for human consumption, it is for program consumption. The output of REST call is usually consumed by a program.

RESTful systems usually communicate over the Hypertext Transfer Protocol with the same HTTP verbs (GET, POST, PUT, DELETE, etc.) which web browsers use to retrieve web pages and to send data to remote servers.

For example, following REST API generates XML response. We can feed this xml response to some other application to process.

http://www.thomas-bayer.com/sqlrest/CUSTOMER

Resource

It is the fundamental concept in REST. It is similar to object in OOPS (Object oriented programming). A set of well defined methods are used to update/create /delete these resources.

Following HTTP methods are used widely to get information about a resource, update, create resource, delete resource.

Method	Description
GET	Retrieve some data
PUT	Update/create data
POST	Create new data
DELETE	Delete data
HEAD	Retrieve headers

Idempotent operations

An Idempotent operation is one that has no additional effect if it is called more than once with the same input parameters.

Method	Is Idempotent	Description
GET	YES	GET is a read-only operation. No matter how many times you call GET request, it has no impact on resource.
PUT	YES	PUT is generally used for update operation. No matter how many times you called update by using same parameters, it has same effect on the resource.
POST	NO	POST is used to create new resource. If you call POST 3 times, it creates 3 resources.
DELETE	YES	DELETE is used to delete resource. It has no impact if you call multiple times.
HEAD	YES	HEAD is read-only operation. It gives response code and headers information.

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