API

Jun 2, 2025

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What is API

An application programming interface (API) defines the rules for how two program communicate with each other. It's usually used in client–server model.

API is like a gateway between client and server. API diagram

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Resource

Resources are the data that software provides to their clients. It can be number, text, image, binary, or any type of data.

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Client

Clients are the role who want to access resources from the server, and thus they need to send a request following API provided by the server.

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Server

On the server, there are multiple resources that the client aims to access. Upon receiving a request, the server places the requested resource into the response and sends it back. In fact, the API is defined on the server side.

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An example of HTTP API

 
[GET] https://www.google.com/
request

The resource in the response is HTML file.

<html>
    <head>...</head>
    <body>...</body>
</html>
HTML
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When did API propose

API originated in the 1940s, but the terminology didn't come into play until the 1960s and 1970s.

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Reference