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What is an API?

An Application Programming Interface (API) is a set of data-driven functions that enables applications to communicate with each other. APIs create a connection between these applications so that data from one server, organization, or internet-based application can be used by another in their functions. The user or client requesting the function might not know what the basis for the code is, and isn’t required to, they just leverage the functionalities by requesting accessibility.

APIs work as a building block for an application to put together the data from an application or operating system. It can be a single function, an interface, or a set of different APIs which users can legally utilize through the parent organization. API documentation works as a guide to let the users or enterprise teams understand the functions of an API thoroughly. APIs not only allow enterprises to access data, they also hide the complexities of a particular function.

For instance, WhatsApp allows users to mark their location on Google or Apple maps which are embedded in the application via Google and Apple APIs. WhatsApp could design a map from scratch, but APIs overcome the hassle of creating a brand new function. The end user enjoys a seamless experience and the application can offer functionality without having to create it.

Applications and software based on APIs have been an essential part of business growth since early 2000. Enterprises strive to create interconnectivity between components, servers, and operating systems, and want to be able to share information. APIs make it possible to meet these goals without having to know the ins-and-outs of every system.

The working of an API is explained in the figure below:

API diagram

Source: https://www.g2.com/articles/api

The value of APIs

An API is responsible for client-server communication. The client makes a request, also known as an API call, to the server to allow the usability of data or function and the application server, in response, allows the retrieval of data. The API acts as a mediator between the communication of such computers and application servers and after receiving the response, transmits it to the source application client. Moreover, most APIs are structured over web standards which is why web APIs are the most common name among APIs. Such web API calls are made through HTTP while, on the other hand, the retrieved message from API to Initial client is in JavaScript Object Notation (JSON) or Extensible markup language (XML) files as such file formats are considered reliable to make changes accordingly.

API diagram

Types of APIs and protocols

In terms of usability, there are some common web APIs that are classified as Open, Private, Partner, and composite APIs.

The open API is open source and is accessible through HTTP protocol. It aids in accessing the data or application services available for all the developers. Private or internal APIs are the APIs designed specifically for a closed environment and cannot be accessed by any other user except the teams of the different environments in a specific organization.

Partner APIs are APIs that are also open source but are limited to be shared among business partners typically on a contract basis. However, the access to the partner API still requires going through an agreed upon procedure to get access to login credentials. Lastly, a combination of several services or variable data in a single API call is referred to as Composite API. It is a utility for users who desire to get information.

API specifications

API types are distinguished based on certain protocols over web services. A web service is a system that uses the URL over WWW allowing access to specific services. Such protocols are destined to regulate the web services between different applications which include the different programming languages, different operating systems, or technologies to establish a seamless connection with each other.

API protocols include Remote Procedure Call (RPC) which is specifically imposed to interact between the applications based on client-server and the function call will be responsible for response and requests between the two. Simple Object Access Protocol (SOAP) is the oldest protocol for web APIs but still has a wide range of usability. This protocol is based on the creation of XML documents which is a way to communicate with the remote server. The main function of SOAP is to interpret the structure of messages being transmitted using HTTP and SMTP protocols and the methods used for client-server communication allowing SOAP to be used in almost every operating environment. 

Representational State Transfer protocol, or REST, is the most widely used API protocol as it relies upon the client-server approach which isolates both of an API's front and backends. REST promises stateless usability meaning it does not store responses or data and offers flexible development.

Efficient data loading and fast time to market due to the increasing adoption of mobile phone applications were needed and GraphQL was introduced for such purpose. It is used for the simplification of data aggregated from multiple sources aiding developers to use one API call to access all the data from different sources.

gRPC is a framework used to directly access the call methods like GET, PUT, etc. which helps in creating distributed applications as well as services. Unlike SOAP or REST, it uses protocol buffers to stack the data sequentially as Interface Definition Language. gRPC is used for connectivity between microservices due to its high performance and availability in multiple languages.


APIs make it possible to gather information and data in a faster, more convenient way. APIs allow applications to interact with other applications, making it easier for end-users to utilize both applications or information based on web APIs.

Macrometa has ready to go industry solutions or customized that leverage APIs for seamless customer experiences and operational efficiency, contact a solutions expert to learn more.

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