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API - Application Programming Interface

API - Application Programming Interface

Today, we use mobile apps for almost all purposes. The purpose ranges from simply sending a message to checking cricket scores online. Application Programming Interface (API) is used to communicate between apps and to access and fetch the required information.

What is an API?

API is the abbreviation of the term Application Programming Interface. It is the software responsible for the connection for the communication and information exchange between two apps. API connects two devices or programs in order to facilitate the exchange of information between them. It is the interface that serves the other parts of the software. The API specifications are the standards or documents designed to describe the creation of such connections. If a computer system meets these standards, then it is said to expose an API. The specification or implementation both are known as the API.

History of APIs

The concept of the API has been there since an early age. The implementation of API has seen various transformations over the years. The only difference has been the way in which the API was accessed and implemented.

In the 1990s the Salesforce launched the web-based API that acted as the sales automation tool. It began the SaaS Revolution, which emphasised software as a service concept. The World Wide Web also encouraged the new way of delivering the software and built the infrastructure to accommodate the new system.

The existence of the API can be traced even before the introduction of the World Wide Web and the Internet. It was first used to provide a service for a limited area. It connected the computer networks in that limited area.

API has a bright future with users and programmers all over the world are using and creating apps that are hosted on the World Wide Web. The function of the API is to enable the API provider to expose the services. Therefore, the external systems call API providers and access the services.

Web APIs

Web APIs provide services such as web notification and storage. These APIs can be accessed through the HTTP protocol. Different APIs differ in the level of security and privacy that they offer. It is possible to combine multiple web API to form a composite API. It is also known as a collection of data or service APIs.

API - Application Programming Interface

Types of Web API

The various types of web APIs are as follows;

  1. Open APIs: It is also known as the external or public API and is the API that has minimal restrictions for the user. These sometimes require registration or API key or sometimes are completely open. These are meant for external users to access data. Therefore, the developers can access the data without the registrations.
  2. Internal APIs: Internal APIs differ from open APIs as these are hidden from external users. These are useful for businesses and are used in a company to share resources within the company. It facilitates different sections and departments of the company to access each other's data. Internal APIs are useful in providing a standard interface for the connection of multiple services in a company.
  3. Partner APIs: Partner APIs are very much similar to open APIs. The only difference is that these feature restricted areas that are controlled by an API gateway, a third-party gateway. These APIs are used for specific services, such as the paid service on any software.
  4. Composite APIs: Composite APIs are unique as they facilitate the developer to access several endpoints in one call. It may have different endpoints for a single API or multiple data sources and services. Composite types of APIs are useful when there is the need to access data from multiple services for the completion of a single task. The composite APIs have three major benefits, which are as follows;
    1. It reduces the server load
    2. Improves the performance of the application
    3. Fetches multiple service data in a single call

API Architectures and Protocols

There are specific rules for API calls, and these are defined by the API protocols. API protocol gives the accepted commands and data types according to the rules. The protocol constraints differ according to the API architecture.


REST is one of the most well-known API architectures. These are some of the principles that the API must adhere to, for being a REST API;

  • Cacheability
  • Client-server architecture
  • Layered System
  • Statelessness


JSON-RPC and XML-RPC both use JSON and XML, respectively, to encode its call. RPC is also known as Remote Procedural Call Protocol. One result is expected from multiple parameters. Following are the features that differentiate it from the REST;

  1. Unlike REST, these are intended to call methods. REST transfers the documents and works with resources.
  2. The URI does not contain any information in its parameter. Unlike REST, URI only identifies the server.


SOAP is also known as Simple Object Access Protocol. It is well-established and is intended to be extensible, neutral, and independent. Following are some of the specifications of the SOAP;

  1. Extensible Model
  2. Message Construct
  3. The Processing Model
  4. Protocol Binding Rules

Although both are competing standards, it is possible to build RESTful API using SOAP protocols.

The Evolution of the API

The usefulness of the World Wide Web and its possibilities were well known at the beginning of the internet era. Hence, companies started transforming the method of providing products and services in a virtual store.

Initially, SOA (Service Oriented Architecture) was the most popular model for the distributed systems. However, it had the limitations of the organisational boundaries. Later, tech experts realised the need to cross the organisational boundaries and hence soon they started publishing the data over the World Wide Web. Therefore, it no longer had any organisational boundaries. It unitised data from multiple sources and presented valuable insights before the customer.

Example of an API

The most common example of API is searching for information on the internet using an app. If you use an application for a particular purpose, you use the internet. A connection is established between the internet and the application. The internet provides data to the server; it retrieves data, processes the information, and sends it back to the phone. The task of the application is to interpret data and present it to the user in a readable format. This process is facilitated using API.

The concept can be explained better with the help of an example. When you go to a restaurant and order food, the food comes from the kitchen. Hence the kitchen is the system. Your table is the place where the response is delivered. However, to deliver food on the table, there must be a channel of communication between the table and the kitchen. The waiter or API acts as a messenger between the table and the kitchen. It takes requests from you and tells the kitchen, which is a system, what has to be done. Then, the waiter delivers the response to the user, which is food in this case.

Another real-life example of API is online flights booking. Similar to the previous example of a restaurant, there are many options of cities, return and departure dates, and cabin class. While booking a flight ticket, you select variables including the cabin class, departure city and date, and return city and date. All the options and data of the flights and the cost of the ticket are displayed on the airline website where you book the ticket. Therefore, you need to interact with the airline databases.

However, suppose you use another travel service website that collects the data from various databases and presents it to the user. In that case, the travel service acts as the API of the airline. Like a waiter in the restaurant, the online travel service will provide options and aid in booking tickets. It does so by collecting the information from the databases. The API will collect the airline's response to your request, deliver it to an online travel service, and present it to you. In this way, you will be able to fetch the most updated information regarding your booking and flight. The data provided by API will be most relevant and helpful for the user.

Therefore, the purpose served by the waiter in a restaurant is the same as that of the online travel service, and both of them are API. Hence, API is crucial for the communication between two systems.

A layer of Security in API

Whenever we use an API, the server is not completely exposed to the device, neither the device is completely exposed to the server. The communication between them takes place through small packets of data that share only the necessary data. For example: While ordering food, you place your order that includes your requirements, and the restaurant puts forward their requirement. Hence you complete your order and get the meal delivered.

APIs have become so useful that companies generate revenue using APIs. Some of the companies that make money using APIs are Amazon, eBay, Expedia, Google, and The APIs comprise a valuable part of the businesses by generating revenue for them. The marketplace of APIs is known as the 'API economy'.

The Modern API

API has been described as a connectivity interface for an application. However, modern API has different characteristics that have made it more valuable. These are described below;

  • They adhere to the standards which are developer-friendly, easy to access and understand.
  • They are specific in their design, hence can be consumed by a specific audience such as mobile developers. The design of these APIs is such that they are meant to fulfil certain expectations of maintenance and lifecycle.
  • As they are more standardised, they are more disciplined for security and performance.
  • They act as a product rather than the code as a product software has its software development lifecycle (SDLC) of testing, managing, designing, building, and versioning. Additionally, modern APIs are very well documented.

Use of API in Everyday Lives

Application Programming Interface (API) plays a crucial part in the economy. APIs are not easily noticed, but they are almost everywhere in our lives and affect us significantly. API is crucial in sharing data and aids communication between two individuals, apps or devices. Following are some of the common daily life functions of API.

  1. Weather Monitoring
    Weather monitoring is one of the most common daily life applications of API. The weather update can be seen on Google Search, smart home devices or Apple's Weather app. whenever you search for the weather of your city using any of these platforms, you'll see an instant result. For example, although Google doesn't do Business in weather, you will get data immediately if you search on Google. It is because Google takes data from a third party using API. After getting this data, Google reformats it and presents it to the user. Many APIs have weather data functionality and are crucial in providing weather conditions and forecasts.
  2. For Logging in
    APIs are also helpful for logging into accounts such as Facebook, Google, Twitter, Github, etc. It helps in accessing the functionalities in these accounts after you log in.
    API does not directly login into a user's account as it would pose a threat to security and privacy. Applications use the API of platforms to authenticate the user with each login.
  3. Payments
    The payment functionality is also built using APIs. Using APIs, it is ensured that the application is only exposed to the necessary data rather than the sensitive data. API prevents the apps from accessing the unintended data and helps it achieve the set objective.
    The working of the payment system is similar to the login functionality. After the user sends the pay command to the application, he sends an order with the payment amount. Additionally, he also adds other relevant information. A pop-up will then confirm the payment by authenticating the user. Subsequently, the API sends payment confirmation to the application and hence the user.
  4. Bots
    Bots are another everyday application of the API. For example, there are many Twitter Bots which are Twitter accounts that carry out functions such as a tweet, follow and send messages directly with the order from the software. Some of the Bots are listed below;
    • TinyCare Bot: It has the function of reminding the user to drink water, stretch, get fresh air, etc.
    • Grammar Police: Rectifies the grammar mistakes of the users and makes corrections accordingly.
    • Netflix Bot: Tweets content-related updates from Netflix.
    These are Twitter API powered bots. The API tells the bots about specific platform details or events. Moreover, it also allows users to execute actions such as tweeting, following.
  5. Bookings
    Travel bookings are another domain where API is of huge importance. Online travel services collect information from third party APIs and present it to the user. The information is useful for the user to choose and proceed with the bookings.

The Future of APIs

APIs are necessary tools and have a bright future with the programmers developing new applications that increase users. The API providers play a crucial role in serving the API customers with event-driven APIs. Following are some predictions about the API economy and the development of API.

Improved API experience on the mobile devices

The network layer of TCP/IP protocol will face a complete revamp for better transformation packets under low and fluctuating network coverage. It is possible with the introduction of HTTP3. This will enable the app developers to improve their time to market as they can incorporate more APIs on the mobile apps. Therefore, the performance of the mobile applications will improve even if there is patchy coverage. It is because accessing APIs will become faster.

New Business models around event-driven APIs

The API providers play a crucial role in serving the API customers with event-driven APIs. It means that there is a shift in the business logic from the API provider's end to the API customer. For example, while you book a ride on Uber, the app automatically assigns the drive and sends you the details. Hence, this is an event-driven API taking your decision behind the scenes, with the aim to serve you.

Other expected development in the API field are;

  1. Better Standardisation for APIs
  2. Rise in Microservices for Delivering APIs
  3. API driven architecture for end-user Apps
  4. APIs as Information Superhighway for Enterprises

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