An API, or Application Programming Interface, is a set of rules and protocols for building and interacting with software applications. APIs enable different software systems to communicate with each other, allowing them to share data and functionality. They are essential in modern software development, facilitating integration and interaction between various services and applications.

• Application Programming Interface (API): A set of defined rules that explain how computers or applications communicate with one another. APIs serve as an intermediary layer that processes data transfer between systems.

• Web APIs: These are APIs that can be accessed over the web using HTTP/HTTPS protocols. RESTful APIs fall under this category.
• Library APIs: These are APIs provided by software libraries to enable interaction with the library's functions.
• Operating System APIs: These APIs allow applications to interact with the operating system.

• Endpoints: Specific URLs where API services can be accessed.
• Methods: The actions that can be performed (e.g., GET, POST, PUT, DELETE in RESTful APIs).
• Request and Response: The data sent to and received from the API.

Consider a weather application that needs to display current weather information. Instead of collecting and processing weather data itself, the application can use a weather API to fetch the required information.

In this example:

• The request is made to the weather API endpoint with the city parameter set to "London" and units set to "metric".
• The response contains the weather data for London, including temperature and description.

Task: Make a simple API request to a public API and interpret the response.

1. Choose a public API, such as the JSONPlaceholder API (https://jsonplaceholder.typicode.com/).
2. Use a tool like Postman or a simple HTTP client to make a GET request to the following endpoint:

   GET https://jsonplaceholder.typicode.com/posts/1
   

3. Observe the response and identify the key components (status code, headers, body).

Request:

Response:

Analysis:

• Status Code: 200 OK
• Headers: Various headers including content-type.
• Body: JSON object containing the post details.

In this topic, we have covered the basics of what an API is, the different types of APIs, and the key components that make up an API. We also looked at a practical example of an API request and response to solidify our understanding. This foundational knowledge will be crucial as we delve deeper into the principles of designing and developing RESTful APIs in the subsequent modules.