REST API Definition: Understanding the Basics of REST APIs

By |2022-05-16T09:08:22+00:00January 28th, 2020|

‘What is REST API and how does it work?’ is a commonly asked question.

An API (application program interface) is a set of rules that enables different programs to communicate with one another. It outlines the appropriate way for a software developer to compose a program on a server that communicates with various client applications.

API integration refers to a couple of applications (two or more) interconnected through their APIs to exchange data and perform a joint function, thus, enabling interaction between applications. Now that we’ve defined API, let’s move towards REST APIs. Various websites like Amazon, Google, Facebook, LinkedIn, and Twitter use REST-based APIs that allow users to communicate with these cloud services.

This will dive deep into the REST API definition and cover all it’s basic aspects, including what does REST API stand for,  REST API principles, REST API methods, and more.

Find out:

What is REST API?

In 2000, Roy Fielding defined REST as an architectural style and methodology frequently used in internet services development, such as distributed hypermedia systems.

Full form of REST API is Representational State Transfer Application Programming Interface more commonly known as REST API web service. It means when a RESTful API is called, the server will transfer a representation of the requested resource’s state to the client system.

For instance, when a developer requests Twitter API to fetch a user’s object (a resource), the API will send back the state of that user, their name, followers, and posts shared on Twitter. This is possible due to API integration projects.

This state representation can be in JSON, XML, or HTML format.

REST API definition

(Source: Seobility)

Typical data transfer protocols, such as SOAP (Simple Object Access Protocol), offer excellent data security and integrity capabilities. Moreover, SOAP offers in-built retry logic to compensate for unsuccessful communications. But such protocols are also tough to work with. RESTful API is a simpler alternative that has developed exponentially in the past few years. People often get confused regarding REST standards. Compared to SOAP, older web services, REST is more flexible and easy to implement.

REST is usually preferred over the more robust SOAP as the former uses lesser bandwidth, making it more appropriate for the world’s comprehensive web services. It uses HTTP protocol to fetch data or carry out operations in several data formats (like XML and JSON); it allows for quicker processes.

Consequently, SOAP uses XML data transfer, defining operations as unidirectional WSDL ports with several process instances sharing the same procedures. In REST, operations are described in messages themselves. Moreover, there’s a single direction for each process instance.

Another difference between SOAP and REST lies in how these protocols are coupled. SOAP is tightly coupled, whereas the latter is weakly coupled. The weak coupling means modules are independent, and variations in one don’t disturb the operation of others. As a result, there’s flexibility and reusability when modules are added, substituted, or adjusted. On the other hand, tight coupling means that modules tend to be codependent. So, variations in one module can have a system-wide effect. All these differences are what make API RESTful.

Several applications and projects are using REST APIs to transfer data, and businesses are increasingly embracing RESTful web services to enjoy horizontal growth.

How Does a REST API Work?

REST determines the structure of an API. Developers oblige to a specific set of rules when designing an API. For instance, one law states that linking to a URL should return some information.

Every URL is known as a Request, whereas the data returned is known as Response.

REST API breaks a transaction down to generate a sequence of small components. Every component addresses a specific fundamental aspect of a transaction. This modularity makes it a flexible development approach.

A REST API leverages HTTP methods described by the RFC 2616 protocol. It uses the following HTTP requests:

  • GET request to fetch data
  • PUT request to alter the state of data (such as an object, file, or block)
  • POST request  to create data
  • DELETE request to eliminate it

Different HTTP verbs or status codes used by REST APIs can be seen here.

What are RESTful APIs Used For?

To better understand what is RESTful API, what is api used for, how it works, and the definition of Rest API, lets consider an example.

Suppose you want to watch video tutorials about ‘data integration’ on YouTube. You go to YouTube, type ‘data integration’ into the search field, press enter, and a list of videos about data integration appears. Right?

A RESTful API works similarly. You seek out something and a list of results returns from your requested service.

In the REST technology, the assumption is that all calls are stateless. This means the REST service can’t retain anything between executions, making it beneficial in cloud applications. This is because stateless constituents can be easily reassigned in case of failure. Moreover, they can be easily scaled to consider load variations. That’s because any request can be sent to any instance of a constituent.

As no data can be retained that has to be recalled by the subsequent transaction, REST is the desired protocol for internet communication. As stated earlier, the REST API technology is also helpful in connecting to cloud applications, as accessing a service via an API needs adjustment in the URL interpretation.

Similarly, REST API can also be used for mapping data from a cloud platform to a data warehouse or vice versa.

REST API Glossary for Key Terms

Before diving into the guiding principles of designing REST APIs, let’s briefly discuss three key API terms:


The client is a hardware or software that uses the API made accessible by a server. For instance, when you visit Facebook’s website, your browser is the client that calls Facebook’s API and utilizes data sent back to display info on your screen.


A resource can be any object the API can offer info about. For instance, in the case of a Twitter API, a resource can be a user, hashtag, or any media type like a picture. Every resource has a distinct identifier that can be a name or number.

The resource is the primary abstraction of information in REST. REST API uses a resource identifier to recognize the specific resource involved in the communication between different elements.


A server is any system that contains resources that the client wants. When it receives client requests, it provides the content to the client using the API interface. The server will only grant a representative state of the source and not complete access to the client.

An excellent example of this is when a mobile app shows YouTube videos through its interface. It uses a REST API to call the video content from YouTube without hosting it on its system.

REST API Features

Here is a list of features that make it the most efficient data and application integration.


REST API offers excellent scalability. As clients and servers are separated, a product can be scaled by a team of developers without much trouble.
Plus, it is easier to integrate REST with present sites without refactoring website infrastructure. This allows developers to work faster instead of spending time reworking a website from scratch. As an alternative, they can merely add extra functionality. This makes it the most used method of integration.

Flexibility and Portability

Users can easily communicate even if the REST client-server is hosted on different servers, offering an essential benefit from management’s perspective.


Thanks to the parting between client and server, the REST protocol makes it easy for developments across the different areas to occur autonomously. Moreover, the REST API is adjustable to the operational syntax and platform, offering the prospect to test numerous environments during development.

REST API Design Principles

Now that we’ve covered the basics and learned about the definition of REST APIs, let’s move on to the six REST principles that guide API design:


This REST principle works on the concept that client and server should be isolated from one another and permitted to develop independently. This way, you can improve manageability across numerous platforms and increase scalability by streamlining server components as user interface concerns are separate from the data storage concerns.


As per this REST principle, APIs are stateless, which means calls can be made independent of one another. Moreover, every call includes the data essential to complete itself effectively.

In other words, every request sent from the client to the server must include all the info needed to comprehend the request.


As a stateless API can upsurge request overhead by managing huge loads of inbound and outbound calls, a REST API design should store cacheable data. According to this API design principle, data within a response should be indirectly or categorized as cacheable or non-cacheable.

If a response is cacheable, the client cache is provided the right to recycle that response data for similar requests in the future.

Uniform Interface

To decouple a client from the server, you need to have a unified interface that permits autonomous development of the application without tightly coupling its services, models, and actions to the API layer itself.

This design principle streamlines the whole system architecture and enhances the visibility of communications. To attain a uniform interface, several architectural controls are required to guide the performance of the elements within the REST API architecture.

REST principles are defined by four interface controls, including identifying resources, managing resources through representations, self-descriptive communications, and hypermedia as the engine of the application state.

Layered System

REST API’s architecture includes several layers that operate together to construct a hierarchy that helps generate a more scalable and flexible application. Due to its layered system, an application has better security as components in each layer can’t interact outside the subsequent layer. Moreover, it balances loads and offers shared caches for stimulating scalability.

A layered REST API architecture system has greater stability because it restrains component performance. so that each component can’t ‘see’ further than the immediate layer with which it is intermingling.

Code on Demand

This REST principle allows for coding or applets to be communicated through the API used within the application.

A REST API definition permits extending client functionality by downloading and implementing coding in the form of applets or scripts. This streamlines clients by decreasing the number of features essential to be pre-implemented.

Most of the time, a server returns static resource representation in XML or JSON format. But when required, servers can deliver executable code to the client.

Astera Centerprise Makes Restful API Integration Easy

REST API integration can be tricky for new developers as you can lose the capability to preserve state in REST, such as within sessions. Therefore, it is significant to comprehend what makes a REST API maintain its state and why these six guiding REST principles need to be considered when designing your API.

Unlike SOAP, REST doesn’t require clients to know the operation semantics before using it. For instance, a client doesn’t need routing information with the initial URL. Plus, ports do not need diverse notifications as clients can have a standard ‘listener’ interface for notifications.

Additionally, with a small number of operations, REST can handle numerous resources, making it simple to build and adapt. We hope the blog cleared any confusion about REST API, from its basic API definition to how it works.

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