What is an Application Programming Interface (API)?

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Application programming interface -رابط برنامه نویسی کاربردی -API

The existence of a user interface (UI) has made it easy to access different parts of a software. In fact, UI is the interface between the logic behind the software and the user who intends to use it. But can a software communicate with another software using User Interface (UI)? From the word User, we can conclude that: “No, such a possibility is not directly available”.

This is where “API” or Application Programming Interface steps in and solves this problem. In this article, we intend to familiarize you more with APIs and also introduce you to the API designed by Bigpro1.

A simple example​

We express the importance of using the application programming interface with a simple example:
Imagine that you need to create a model from your data and then use that modeled data in your application. But you may not have enough knowledge, money and manpower to do this. Acquiring knowledge in this field undoubtedly requires a lot of time.
But Bigpro1 has solved this problem and made it possible to create a model of data with a few simple clicks. After data modeling in Bigpro1, an 
API will be provided to you and you can use them in your application.

What is an application programming interface or API?​

API stands for Application Programming Interface. Of course, sometimes it is better to call it “software programming interface”. APIs are responsible for communicating between two executable codes in different locations. In other words, an application programming interface is a way for software to talk to each other.

In another definition, it can be said that APIs are an abstract layer between two executable programs that provide specific accesses and connections from the server to the client. In general, in computer science, if you face a problem that is complicated to solve, it is enough to use abstraction layers and reduce the complexity.

Think of abstraction layers as columns, so that the parts above the abstraction layer depend on the components below it. The abstraction layer makes it possible to make rules that work without considering the details of the underlying layers.

An example of an abstraction layer is the ISA (Instruction Set Architecture) layer in computer architecture, which makes programmers write their programs and manage hardware without considering the hardware implementation details by using the assembly language of that architecture.

Obviously, the APIs themselves are implemented by programming code. One of the goals of APIs is to prevent the complexity of implementing some algorithms. For example, the algorithms of decision support systems are complex and their implementation requires a certain level of knowledge; But in Bigpro1, it is possible to use APIs of the decision support system. When we send a request to an application through an API, we are not supposed to know what functions are being called in that application and how they work, we just need to reach our main goal as quickly as possible.

You probably assume that APIs are always used in websites and online applications; But this thinking is wrong. We will discuss this further.


Obviously, applications that use APIs can be anything other than network-based software.

* The image below shows a high-level view of the web-based API:
Application programming interface

As you can see, a software can connect to an IP through the Internet and receive services. It is quite clear that the API plays the role of an interface between the application and the web server. Now look at the image below:

Application Programing Interface

As you can see, there is no web server and Internet here, and Windows programs can access different parts of the system through the APIs provided by Windows. Here,APIs play the role of an intermediary between the application software and the lower levels of the operating system.

If these APIs did not exist, the programmer would have to communicate directly with the lower levels of the system, and this task is not easy for ordinary programmers.

In the picture above, Application can be considered a client, and the client can be a driver or operating system kernel.

In general, the application programming interface is an interface between two software (client and server) that determines the protocols for their communication with each other.

Types of web APIs​

In general, APIs can be divided into different aspects. In terms of accessibility, APIs can be divided into 4 categories, which are listed below:

Public API:

This type of API (also known as open API) can be made available to all developers and companies. Companies offer these APIs according to their business strategy. While some public APIs are free, others require a subscription fee. 

Partner API:​

Partner APIs are designed for specific companies outside of the developer company. If we consider the manufacturer company X, only some partners of X can use the partnership API. Usually, these APIs include important features and therefore have strict and clear usage rules and also have strict authentication mechanisms.

Private API:​

Because private APIs aren’t documented in a publicly released software development kit, they are often completely hidden from the public. Developers working for the company can use these APIs, but external developers can’t. Using APIs for internal data transfers is regarded as more efficient, secure, and traceable.

Composite API:​

A composite API provides a combination of different APIs, in a specific order, that are related to each other and can be useful to prevent complexity and increase efficiency.

Types of APIs in terms of use cases​

APIs can be designed and implemented for various tasks. These tasks are not limited to retrieving information from databases and can be implemented in other areas as well. The most common examples of their use are listed below:

APIs available in operating systems:​

This application programming interface allows operating system software to have safe and easy access to system resources without the need for direct access to SysCalls. An example of this is the win32 API in Windows.

Database APIs:​

They allow applications to communicate with the database management service.

Remote APIs:​

Remote APIs define a method through which two programs on different machines can communicate and execute code remotely. In other words, a software on my system can access your system resources. Since most remote API standards communicate through networks, especially the Internet, most standards are implemented with the Web. For example: Java Remote Method Invocation API.

Web APIs:​

Nowadays, when we hear the name of the application programming interface, without a doubt, Web API comes to our mind (the most used is in this category). By using Web API, information can be sent and received using the HTTP protocol and with certain rules. These rules can include the sending method in the HTTP protocol and the markup language used for data formatting, etc. This architecture is based on the client-server architecture and is usually implemented using the GET method.

Types of web API protocols​

Since the most common use of APIs is in Web applications, we will briefly review the types of Web APIs.

When we intend to use a web API, we must know the rules of information exchange between the server and the client. The format of the sent and received information must be clearly defined. In theory, any kind of implementation can be designed to communicate. Anyway, its most famous protocols are:


Representational state transfer (REST) is a client/server based protocol that separates front end and back end using API. The REST protocol does not store any data during requests. These API responses can be stored for a short time. Their markup language can be JSON or XML or even plain text.


The remote procedural (RPC) is a simple way to send parameters and receive results by calling an executable process. This is while in REST API we can only send and receive data and resources such as documents. RPCs can be used using JSON and XML.


Simple Object Access Protocol (SOAP) is a messaging protocol designed by the World Wide Web. The common language for using this protocol is XML and it is widely used in the Internet. SOAP protocol can be used in HTTP and SMTP. The SOAP protocol can be easily extended and modified.

What is API documentation?

It can be said that the most important part of designing an application programming interface is to create a set of complete and understandable documentation. Even if the API is private, detailed resources should be available for company employees to study the API’s capabilities. When you are studying a programming language, or learning a framework, you will definitely come across the word “Documentation”. In general, documentation contains official and detailed information about a specific subject.

API documentation also contains detailed information about how to use the API, which is written by the API designer.

How to use API?​

In fact, this question regarding APIs cannot be answered easily, because as you read earlier about APIs, there are different types of APIs in terms of use cases, each of which can be considered individually and expertly. But it should be noted that studying the API documentation is the first step to learning.

For example, if you plan to use decision support systems in your program and you plan to use BigPro1 API, you can learn how to use the relevant API by reading its documentation. In general, the most important step to use an API is to read its documentation.

The documentation of an API can be very large and complex or very small and simple.

Advantages of using API

  • As we said at the beginning of this article, API can prevent complications. But this is not the only benefit of using APIs. Some of the benefits of APIs are listed below:
  •         Prevents complications
  •         Provides security
  •         Creates coordination between programs
  •         Using API functions in an operating system like Windows can reduce the size of the program and increase the efficiency
  •         Simplifies app development for startups 

What is EndPoint in API?

An EndPoint can be thought of as a digital location from which the API extracts requested resources. An EndPoint can be a series of files or a set of activities. Endpoint is part of API while API has a broader concept than EndPoint.

A commonly mentioned item in API documentation is a list of EndPoints. Since resources and applications are on EdnPoints, securing them can be an important and challenging issue. As we mentioned earlier, one of the benefits of APIs is security. Apart from the fact that we need to implement mechanisms to ensure the security of the API itself, we need to restrict access to some resources for some users through the API itself.

For example, if we have an API that is supposed to allow us to search the site’s database, it is important to consider that the search strings should not contain SQL commands, or if they do, the result should not be displayed to the user.

An EndPoint can be a URL on a web server and can be accessed directly. For example, you can get information about a tweet using the following EndPoint:


Web-based API testing methods

  • In order to be able to test and use a web-based API or EndPiont, there are different send and receive methods. The most widely used web APIs are in the REST type, and this type uses the HTTP protocol. This protocol is so detailed that books have been written on the subject and various versions have been reviewed. However, we are not going to go into the details of this protocol and only list the API test methods that can be used to send and receive information:
  •       GET: to receive data
  •      POST: To send data
  •      PUT: To update data
  •       DELETE: To delete an existing data

Knowing these methods, API testing is a simple task.


The most used are the first two methods, GET and POST. Since HTTP is a one-way protocol, (meaning any time data is either being sent or received, it’s not synchronous) we are always sending and receiving data. That is, every question must contain an answer.

Examples of application APIs

There are many APIs, each of which is designed for specific purposes and can increase the speed of production and prevent many complications. In this section, we collected examples of useful APIs for you:

Decision support system APIs in Bigpro1

Fortunately, in Bigpro1, it is possible to use the modeled data in your own program by modeling the desired data.


To do this, you can enter your user profile in Bigpro1 and then select the data modeling option from the data mining section. After modeling, select it by viewing the modeled data list. Then, by creating a decision support system, you can access the API related to the modeled data. All necessary technical information is placed in the same section.

Windows API

As we mentioned earlier, APIs aren’t just for the web. This application programming interface is very practical and is widely used by Windows programmers directly and indirectly. Many things cannot be done directly with a programming language like #C and can only be done with Windows API functions. For example, it is not possible to easily detect the connection of peripheral devices or it is not possible to use system hooks.

Telegram Bot API

One of the most important facilities that Telegram provided to its users was its bots. Telegram created many opportunities for programmers so that any programmer can design even a completely personalized Telegram. Interesting things can be done using Telegram bots; For example, game creation, group management bot, bots connected to other APIs, etc.