REST is an architectural style which stands for Representational State Transfer.

An API for a website is that allows two software programs to communicate with each another. A REST-Ful API is an application program interface that uses HTTP requests to GET, PUT, POST and DELETE data. REST is a logical choice for building APIs that allow users to connect and interact with cloud services. RESTful APIs are used by such sites as Amazon, Google, LinkedIn and Twitter.

A RESTful API explicitly takes advantage of HTTP methodologies defined by the RFC 2616 protocol. They use GET to retrieve a resource; PUT to change the state of or update a resource, which can be an object, file or block; POST to create that resource; and DELETE to remove it.

Why REST ?

REST systems aim for –

  • Fast performance –  component interactions can be the dominant factor in user-perceived performance and network efficiency
  • Reliability – is the resistance to failure at the system level in the presence of failures within components, connectors, or data
  • Scalability – ability to grow, by re-using components that can be managed and updated without affecting the system as a whole, even while it is running.
  • Simplicity of a uniform Interface
  • Visibility of communication between components by service agents

The REST architectural style describes six constraints. These constraints, applied to the architecture, were originally communicated by Roy Fielding in his doctoral dissertation in 2000 and defines the basis of RESTful-style. If a service violates any of the required constraints, it cannot be considered RESTful.

The formal REST constraints are as follows:

  1. Client-Server–  The client-server constraint works on the concept that the client and the server should be separate from each other and allowed to evolve individually and independently. In other words, I should be able to make changes to my mobile application without impacting either the data structure or the database design on the server. At the same time, I should be able to modify the database or make changes to my server application without impacting the mobile client. This creates a separation of concerns, letting each application grow and scale independently of the other and allowing your organization to grow quickly and efficiently.
  2. Stateless :Each request from client to server must contain all of the information necessary to understand the request, and cannot take advantage of any stored context on the server. Session state is therefore kept entirely on the client.
  3. Cacheable : – Cache constraints require that the data within a response to a request be implicitly or explicitly labeled as cacheable or non-cacheable. If a response is cacheable, then a client cache is given the right to reuse that response data for later, equivalent requests.
  4. Uniform interface: – The uniform interface lets the client talk to the server in a single language, independent of the architectural backend of either. This interface should provide an unchanging, standardized means of communicating between the client and the server, such as using HTTP with URI resources, CRUD (Create, Read, Update, Delete), and JSON.
  5. Layered system: As the name implies, a layered system is a system comprised of layers, with each layer having a specific functionality and responsibility. If we think of a Model View Controller framework, each layer has its own responsibilities, with the models comprising how the data should be formed, the controller focusing on the incoming actions and the view focusing on the output. Each layer is separate but also interacts with the other. In REST API design, the same principle holds true, with different layers of the architecture working together to build a hierarchy that helps create a more scalable and modular application.
  6. Code on demand (optional) : Perhaps the least known of the six constraints, and the only optional constraint, Code on Demand allows for code or applets to be transmitted via the API for use within the application. In essence, it creates a smart application that is no longer solely dependent on its own code structure. However, perhaps because it’s ahead of its time, Code on Demand has struggled for adoption as Web APIs are consumed across multiple languages and the transmission of code raises security questions and concerns. (For example, the directory would have to be writeable, and the firewall would have to let what may normally be restricted content through.)





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