To understand the REST API, we need to get a thorough understanding of APIs first. API stands for Application Programming Interface. It is simply a way for computers to talk to each other. API is a set of rules and protocols that allows different applications to communicate and interact with each other. It defines the methods and data formats (JSON, XML etc) that applications can use to exchange information in the web. Basically it acts a middle man or a server of data making it easier for developers to work with data available in the web and create efficient software solutions.
And the most common standard used by most mobile and web application to talk to the server is called REST API. The full form of REST is Representational State Transfer.
Any APIs that follows the REST standards are called RESTful APIs. Real life example of RESTful API include Twilio API, Stripe API and Google's Directions API.
These APIs must adhere to a set of constraints(rules) that define how the API should be designed and interact with other computers(servers). It is not a specification, but rather loose set of rules for building web APIs. Some of these basic principles(rules) of a RESTful API that has made it so popular with developers and organization when building scalable web services include:
1. Uniform Interface:
A RESTful API must have predictable and consistent interface. This allows APIs to evolve separately in both client and server side. Some of the components of the interface include: URIs, HTTP methods and media types such as JSON and XML.
2. Client-Server Architecture:
REST API must have a separate client and server entities that communicate over a network in which client is responsible for user interface and server is responsible for processing requests, managing available resources and storing data. With this kind of separation of client and server allows for more flexible and scalable system architecture.
3. Statelessness:
A RESTful implementation should be stateless; meaning two parties (client & server) don't need to store any information about each other. And each request and response is treated as new one and are independent of other request-response. This leads to web application that are easy to scale and well behaved.
4. Cacheable:
Cacheability is another constraints in the REST architectural style. Caching allows responses to be stored in client-side which directly facilities other principles of RESTful API like scalability, performance optimization and statelessness. When a response is cacheable, repeated requests for the same resource can be severed from the cache instead of fetching that same resource from the server every time. This also ensures that resources are delivered much faster to clients and allows for optimum utilization of resources at hand.
5. Layered System:
In RESTful architecture, components are organized into layers where each layer has a specific function and these layers can only communicate with certain number of adjacent layers which provides a clear separation of concerns. Different components of a RESTful API can be presentation layer(client), application logic layer(server) and a data storage layer(database). This separation of concerns in a architecture ensure easy scalability if need be, simplified communication and enhanced security.
6. Code On Demand (Optional)
Of all the constraints, code on demand is only optional constraint. Usually, a client can only get data from an API. But this constraint states that, in addition to the data the server can provide the executable code to the client as well. Eg; a JavaScript file that a client can download and run on client side. However, is posses a sever security threat and reduces visibility and this is one of the prime reasons why it is an optional constraints.
Conclusion
Apart from these principles of REST, its wide adoption and standardization by big corporations and well established entities. Along with this it's simplicity and ease of use have made RESTful APIs incredibly popular and preferred choice for many developers and organizations when building mobile and web application.
Nonetheless, it is essential to remain aware of other emerging API standards that are gaining traction in the industry, such as GraphQL and gRPC, that are steadily growing in popularity.
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