What is an API?

Definition

What is an API?

The term API stands for “Application Programming Interface “.

An API is a collection of definitions, commands and protocols that specify the interaction options with a system, application or service.

An API allows two independent software components to communicate with each other in a predefined way and exchange data (in real time). Because the data exchange only takes place via a defined interface, the remaining program components can remain hidden, which significantly simplifies communication between applications.

APIs are used in a wide variety of areas: The programming interfaces of operating systems such as Windows and iOS ensure that programs can be developed and executed for these systems. The PayPal payment service can be integrated into online stores via its API. Components of a complex software system also communicate with each other via APIs.

Explanation

How do APIs work?

APIs can be implemented in a wide variety of ways (see Types of APIs).

Regardless of the implementation, they generally follow a few basic principles:

• API requests by a client
• API responses 
• Authentication and authorization
• API documentation

API requests by a client:
Communication via APIs is usually based on a client-server model, in which a client application makes API requests to a server and receives a response from it. The client uses the commands, parameters and endpoints specified by the API to perform actions such as retrieving or changing certain information.

Answering requests:
After processing the request, the server generates a response that is sent back to the client. This response usually contains either the requested data or information about the result of an operation. Data is often transmitted in JSON or XML format.

Authentication and authorization:
APIs can use security mechanisms such as authentication tokens or API keys to ensure that only authorized applications can access their functions.

API documentation:
A good API is usually provided with detailed documentation to help developers understand and use it correctly. This documentation can include information about available endpoints, supported request methods, parameters, expected response formats and possible error codes.

Classification

Types of APIs

APIs can be differentiated according to various criteria. One of these is their accessibility. Many APIs are only intended for internal communication (private APIs) – within a company or even a single software system.

Other APIs are publicly accessible (public APIs) and in many cases well documented. There are also hybrid models – e.g. APIs that are only made available to customers, business partners or other authorized persons.

It is also possible to differentiate between APIs according to their architectural style and the protocols used for implementation:

• REST
• SOAP
• RPC
• GraphQL

REST: Representational State Transfer (REST) is the leading architectural style in the design of web-based APIs today. It is based on a client-server model, where the client addresses the desired resources using the HTTP protocol. REST defines various criteria that a so-called RESTful API must fulfill, in particular the statelessness.

SOAP: SOAP is a network protocol for data exchange between systems. SOAP also defines an approach for setting up an API and describes how data is exchanged, packaged and secured. Protocols such as HTTP, SMTP or FTP can be used for data transfer, while data is represented in XML format.

RPC: RPC stands for Remote Procedure Call. An RPC API provides functions that can be called by a client on remote systems. This approach is mainly used for private APIs. Data can be represented in formats such as XML (XML-RPC) and JSON (JSON-RPC).

GraphQL: GraphQL is a query language and runtime environment for APIs that supports more complex queries. Clients can specifically address multiple resources in one request. They can also become subscribers and be notified of data changes in real time.

Relevance

Why are APIs so important?

Nowadays, APIs are essential for the development of software, the provision of web services and communication between applications.
The main advantages of using APIs can be summarized as follows:

• Interoperability
• Modularity and reusability
• Ecosystems and partnerships
• Accelerated development and market launch

Interoperability: APIs allow different applications and systems to interact seamlessly with each other, regardless of their underlying implementation or programming language.

Modularity and reusability: By using APIs, developers can access existing functions and services instead of having to implement them themselves. As a result, more complex applications can increasingly be built from individual services, which brings numerous advantages for maintenance, troubleshooting and scalability.

Ecosystems and partnerships: APIs play a key role in creating ecosystems and partnerships between different companies and platforms. By granting third-party providers or independent developers access to certain resources, companies can expand both the reach and the functionality of their products and services.

Accelerated development and time to market: By giving developers access to ready-made functions and services, APIs significantly speed up the development of software applications.

Examples

5 practical examples for APIs

From social media and e-commerce to Industry 4.0 – APIs play a crucial role in networking and interaction between a wide variety of applications and systems.

To illustrate this, we look at a few well-known examples of APIs in everyday private and professional life.

Map services:
Numerous apps and websites integrate maps from Google Maps or other providers to provide directions, location services or similar functions for their users. They can use various APIs for this purpose, including the Maps Embed API for easy integration into websites.

Shipment tracking:
APIs for shipment tracking are relevant for both private individuals and companies. One example are the APIs by DHL.

News services:
APIs from news agencies and media companies allow access to the latest news as well as image and video content. These can then be integrated into websites and other applications. An example for this is the reuters API.

Website logins: Many websites offer functions such as “Sign up with Google” or “Login with Facebook”. These options are also provided by APIs.

Industrial equipment: Industrial machines and devices can not only provide real-time data via APIs, but also receive operating instructions and parameters. With our cloud platform manubes, such API requests can be automated using workflows.