API

A	Application
P	Programming
I	Interface

Allows other programs or application to use functionality that you expose:

• Functions
• Protocols
• Objects

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Weather Data Example

Request:

GET https://www.7timer.info/bin/astro.php
?lon=15.593063
&lat=48.411018
&ac=0
&unit=metric
&output=json

Response:

HTTP/1.1 200 OK
Content-Type: application/json
 
{
  "product": "civil",
	"init": "2023070206",
	"dataseries": [
		{
			"cloudcover": 7,
			"temp2m": 21,
			"rh2m": "63%",
			"wind10m": {
			"direction": "W",
			"speed": 3
		},
		...
	]
}

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API Use-Cases

• Frontend - Backend Communication
• Component Comunication
  • e.g. One Service calls another service
• DaaS

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Frontend-Backend

Using APIs, you can link any software parts, potentially using different technologies, as long as they support the same protocol.

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Component Communication

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Protocols

There are several common protocols used in APIs.

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Usage

From the Postman State of the API Report 2025:

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Attributes of protocols

Protocols …

• allow exchange of messages and information between 2 processes.
  • Processes don’t need to be on the same physical machine. Can be distributed and communicate over network.
• are open to any technology or programming language.
• have a clear specification.