Tuesday, April 12, 2011

RESTful Web Service tutorial: An Introduction for beginners

REST is a term coined by Roy Fielding in his Ph.D. dissertation to describe an architecture style of networked systems. REST is an acronym standing for Representational State Transfer. Representational State Transfer(REST), a software architecture style used in developing stateless web services. While this style may be used to describe any distributed framework that uses a simple protocol for data transmission and no other additional data transfer rules, the most common use of REST is on on the Web with HTTP being the only protocol used here. In REST each service (called “resource” in REST) is viewed as resource identified by a URL, and the only operations allowed are the HTTP – GET (Read), PUT (Update), POST(Create) and DELETE (Delete). You can find this style similar in SQL, thinking of a resource as equivalent to a Table. The main features and constraints of REST architectural style are:
  • Client-Server: A clear separation concerns is the reason behind this constraint. Separating concerns between the Client and Server helps improve portability in the Client and Scalability of the server components.
  • Stateless: All REST resources are required to be stateless. The idea is that the application would be resilient enough to work between server restarts. However, it is not uncommon to see some RESTful web services save states between requests.
  • Caching: Caching is allowed, however it is required that “response to a request be implicitly or explicitly labeled as cacheable or non-cacheable”
  • As there is no interface definition (like in SOAP), it becomes mandatory for a Client and Server to have a mutual understanding of the messages being transmitted between them.
Given that every resource in a RESTful service is represented by a URL, it is easy to write a client for such a web service.
A lot of companies these days (including Amazon and Yahoo!) are exposing their web services in the form of REST resources. At a high level REST is pretty easy to understand, all you’re doing is exposing a web service in the form of a URL. Users can then query this URL, through HTTP methods like GET and POST. REST calls generally return some type of XML or Object Encoding like JSON.

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