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.
REST APIs are commonly used by various websites like Amazon, Google, Facebook, LinkedIn, and Twitter, allowing users to communicate with these cloud services.
This article will give you REST API definition and how it works. We’ll look at some reasons why REST API is becoming a preferred method of communication among users these days. Lastly, we’ll cover the six guiding principles that you must keep in mind to create RESTful API.
REST API Definition Explained
First introduced by Roy Fielding in 2000, REST is an architectural style and methodology frequently used in internet services development, such as distributed hypermedia systems.
REST stands for REpresentational State Transfer, meaning when a REST API is called, the server will transfer a representation of the requested resource’s state to the client.
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 representation of the state can be in a JSON, XML, or HTML format.
Typical data transfer protocols, such as SOAP (Simple Object Access Protocol), offer great capabilities in terms of data security and integrity. Moreover, SOAP offers in-built retry logic to compensate for unsuccessful communications. But such protocols are also tough to work on. REST is a simpler alternative that has developed exponentially in the past few years.
REST is usually preferred over the more robust SOAP as the former uses lesser bandwidth, making it more appropriate for the world wide web services. As it uses HTTP protocol to fetch data or carry out operations in several formats (like XML and JSON), it allows for quicker operations.
Consequently, SOAP uses XML data transfer, defining operations as unidirectional WSDL ports with several process instances sharing the same operation. In REST, operations are defined in messages themselves. Moreover, there’s a single direction for each process instance.
Another difference between SOAP and REST lies in the way these protocols are coupled. In SOAP, there is tight coupling, 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.
Currently, several applications and projects are using REST APIs to transfer data, and businesses are increasingly embracing RESTful web services to enjoy horizontal growth.
How Do REST APIs Work?
To better understand how a RESTful API design works, let’s 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 there appears a list of videos about data integration. Right?
A REST API works similarly. You seek out something and a listing of results is returned from your requested service.
REST determines the structure of the API. Developers oblige to a certain set of rules when constructing the API. For instance, one rule 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 the 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 requests:
- GET to fetch data
- PUT to alter the state of data (such as an object, file or block)
- POST to create data
- DELETE methods to eliminate it
Different HTTP status codes used by REST APIs can be seen here.
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 easily 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 technology is also useful in connecting to cloud applications, as accessing a service via an API just needs adjustment in the interpretation of the URL.
Key Terms
Before diving into the guiding principles of designing REST APIs, let’s briefly discuss two key terms:
Client
The client is the hardware or software that uses the API made accessible by the server. For instance, when you visit Facebook’s website, your browser is the client who calls the Facebook API and utilizes the data sent back to display info on your screen.
Resource
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 main abstraction of information in REST. REST API uses a resource identifier to recognize the specific resource involved in the communication between different elements.
Why Should You Use REST API?
Scalability
REST API offers great scalability. As the clients and servers are separated, the product might be scaled by the team of developers without much trouble.
Plus, it is also easier to integrate REST with present sites without refactoring website infrastructure. This allows developers to work faster instead of spending time reworking on a website from scratch. As an alternative, they can merely add extra functionality.
Flexibility and Portability
Through REST APIs, users can easily communicate even if the client and servers are hosted on different servers, offering an important benefit from the perspective of management.
Independence
Thanks to the parting between client and server, the REST protocol makes it easy for developments across the different areas of a project to occur autonomously. Moreover, the REST API is adjustable to the operational syntax and platform, offering the prospect to test numerous environments during development.
Guiding Principles of REST API Design
Now that we’ve covered REST API definition, let’s move on to the six guiding principles of REST API design:
Client-Server
This principle works on the concept that the client and the 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 the server components as user-interface concerns are separate from the data storage concerns.
Stateless
As per this principle, REST 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 server must include all the info needed to comprehend the request.
Cacheable
As a stateless API can upsurge request overhead by managing huge loads of inbound and outbound calls, a REST API design should be able to store cacheable data. According to this principle, data within a response should be indirectly or clearly categorized as cacheable or non-cacheable.
In case 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.
Applying this 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 architecture.
REST is defined by four interface controls, including: identification of resources, management of resources through representations, self-descriptive communications, and hypermedia as the engine of 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, the 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 architecture system has greater stability because it restrains component performance in a way that each component can’t ‘see’ further than the immediate layer with which it is intermingling.
Code on Demand
This principle allows for coding or applets to be communicated through the API to be 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.
In a Nutshell….
For new developers, using a REST API can be tricky 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 principles exist before designing your API.
Unlike SOAP, REST doesn’t require clients to know the operation semantics before using it. For instance, the client doesn’t need routing information with the initial URL. Plus, ports do not need diverse types of notifications as clients can have a standard ‘listener’ interface for notifications.
Additionally, with a small number of operations, REST can handle numerous resources, which makes it simple to build and adapt.
Originally published at https://www.astera.com on January 28, 2020.
