What is an API and where is it used?

Application programming interfaces (APIs) have revolutionized the way modern software communicates and interacts. They are the foundation of virtually every web and mobile application, allowing them to exchange data and use the functionality of other systems without having to delve into the details of their architecture.

APIs are used in almost every sector of the economy - from e-commerce and banking, to social media and payment systems, to cloud services, the Internet of Things and artificial intelligence. Understanding what an API is and where it is used is nowadays a key knowledge not only for developers, but also for marketing and business professionals and anyone who wants to develop their competence in the field of information technology.

Definition of Application Programming Interface, or what is an API?

API stands for Application Programming Interface, which in Polish means application programming interface. It is a set of well-defined rules, protocols and tools that define how different software components communicate with each other. The interface acts as an intermediary that allows one application to access functions or data provided by another application, so that a programmer using the API does not need to know the internal structure of the system he is connecting to.

Technically speaking, an API is a layer of abstraction that defines the methods that can be called, the data formats to be used, and the communication conventions. More precisely, an application programming interface defines how programs should interact with each other, what parameters and methods are required for the interface to work properly, and what the structure of requests and responses should look like. With this approach, programmers can create new solutions that integrate with existing systems, without having to build all the functions from scratch.

A well-designed application programming interface should, above all, be easy to understand and use, flexible and not require complex documentation. Today's APIs often use the HTTP protocol for communication, making them accessible over the Internet and enabling the development of distributed applications that run on different platforms and devices.

The way programming interfaces work is based on a client-server model, where a client application sends requests to a server, which then processes them and sends back an appropriate response. In this architecture, the API acts as an interpreter - it controls the application's access points, handles external requests and allows feedback.

A key feature of most modern solutions is their statelessness, meaning that each query is independent and contains all the necessary information to process it. This architecture makes systems scalable and easy to maintain.

Standard HTTP methods are used to perform operations on resources.

• GET - is used to retrieve data without modifying it,
• POST - allows you to create new resources,
• PUT - allows you to update existing items,
• DELETE - allows you to delete resources.

Each resource is identified by a unique URL, referred to as an endpoint, which is a specific path to access a specific function or data.

Application programming interfaces come in many different forms and standards that address specific technological needs.

First of all, we can mention REST API (Representational State Transfer), which is the most popular architectural style currently used to design web applications. RESTful interfaces use standard HTTP methods and resources identified by URLs. It is characterized by statelessness (as we have already explained in the API mechanism section), scalability and flexibility in terms of data formats.

SOAP (Simple Object Access Protocol), on the other hand, is a protocol that uses XML format and offers advanced security mechanisms at the message level. It is mainly used in banking, telecommunications and health care, where special data protection is required.

GraphQL , on the other hand, is a state-of-the-art solution that allows customers to specify precisely what data they want to receive, eliminating the problem of downloading too much or too little information. It is ideal for mobile applications and environments with limited bandwidth.

In addition to the main standards mentioned above, there are other types of application programming interfaces, such as Web APIs, operating system APIs and hardware APIs.

The PSD2 directive has opened up the financial sector to new opportunities, forcing banks to provide application programming interfaces that enable authorized third parties to provide payment services. Banking APIs are specialized software that allow third-party companies (fintechs), to use customer data taken from banks to provide payment services.

In accordance with the requirements of the PSD2 Directive, banks have prepared special interfaces in line with a standard developed by entities in the Polish payments sector, called PolishAPI. This API allows third parties to provide the following services: Payment Initiation Services (PIS) - a service for initiating a payment transaction, Account Information Service (AIS) - a service for accessing account information, Confirmation of the Availability of Funds (CAF) - a service for confirming the availability on a payer's payment account of the amount necessary to execute a payment transaction, and Authorization Service (AS) - a technical interface required for the operation of the other interfaces.

What are the services provided by non-banks, thanks to the provision of APIs by banks, that are possible today? Among the most important, we can mention here:

• Instant payments and interbank transfers,
• Account aggregators to manage finances from different banks,
• advanced real-time scoring analysis,
• Automatic algorithm-based savings tools,
• identity verification without traditional documentary methods.

API applications in e-commerce and online stores

Application programming interfaces play a fundamental role in the functioning of today's online stores, enabling automation of processes or integration with numerous external systems.

Implementing an API brings tangible benefits to online merchants in the form of time savings, increased efficiency and streamlined daily business processes. First and foremost, it enables automation of repetitive tasks such as payment processing, inventory updating and shipment sending, which reduces operational costs and minimizes the risk of human error.

The most important applications, thanks to the APIs provided in e-commerce include:

• Integration with payment gateways (Przelewy24, Autopay, PayU),
• Connecting to courier systems and managing shipments,
• Inventory synchronization,
• Automation of price list updates,
• Integration with marketplace platforms (Allegro.pl, Amazon.pl, Erli.pl),
• Connection to ERP and WMS systems.

Internet of Things (IoT) and APIs in smart devices

The Internet of Things (IoT) is one of the fastest growing areas of application programming interfaces, enabling communication between devices without direct human intervention. IoT APIs allow for device integration, providing, for example, data exchange between sensors, controllers and cloud platforms.

Cloud Computing - APIs in cloud services

Application programming interfaces are also the foundation of cloud service operations, enabling management of cloud resources, data storage and computing power. The three major cloud service providers - Amazon Web Services (AWS), Microsoft Azure and Google Cloud Platform (GCP) - already offer very powerful sets of APIs for managing their services.

Artificial Intelligence and Machine Learning - AI APIs

It is also impossible not to mention here the huge impact of making APIs available, on the availability to a wider range of developers of artificial intelligence and machine learning solutions.

Let's just mention Azure Machine Learning, which offers REST APIs that allow the creation of clients using REST calls to work with the service, or Dialogflow, provided by Google, which makes it possible to call artificial intelligence models through a programming interface, which has made it possible, among other things, to integrate various services with voice assistants such as Google Assistant or Amazon Alexa.

Many companies also offer their own chatbots in apps, relying on GPT's Chat API.

Understanding how application programming interfaces work and knowing how to use them are key competencies today for those developing careers in IT. Students majoring in computer science at PJAIT gain comprehensive knowledge covering both the theoretical foundations of APIs and the practical skills to design, implement and document them. The curriculum covers advanced topics related to distributed systems architecture, communication protocols or REST API security against credential stuffing attacks.

Knowledge of APIs is particularly important in the context of big data analytics. Today's analytics systems rely heavily on software interfaces to retrieve, process and exchange huge volumes of information. Big Data analysts use APIs to integrate disparate data sources, automate ETL (Extract, Transform, Load) processes and create data pipelines that connect cloud systems to analytical tools.

API competencies also include the ability to read and create technical documentation, which is crucial for effective collaboration in development teams. Well-organized API documentation makes integration seamless and enhances the developer's experience.

Application programming interfaces are an integral part of today's technology landscape, enabling seamless communication between disparate IT systems. APIs make it possible to create complex digital ecosystems in which web applications, mobile applications, cloud services, payment systems, social platforms and IoT devices work together efficiently and securely. 

The importance of APIs will continue to grow as technologies evolve, characterized by the complexity of information systems and the increasing need to integrate diverse platforms and services. For those developing a career in information technology, such as students majoring in computer science, knowledge of application programming interfaces is the foundation for building modern, scalable and secure digital solutions.