1. What are APIs?

Application Programming Interfaces

An Application Programming Interface (API) is a contract that allows code to talk to other code. APIs are the building blocks of modern software because they allow for sharing of resources and services across applications, organizations, and devices.

• APIs help developers integrate exciting features and build automation without reinventing the wheel.
• APIs allow enterprises to open up their product for faster innovation.
• APIs can be products themselves (SaaS).

APIs - A Digital Restaurant

You can think of an APIs a being like a waiter at a restaurant, serving as a go-between for the customer and the kitchen. A customer who wants soup does not go into the kitchen to cook and they don’t even have to know how to make it. The only have to know how to ask the waiter for soup, expecting the waiter to bring back soup.

APIs work the same way, but there are different names for the players involved:

Networking term	Description	Restaurant analogy
Client	The requester. Ex: browser, web app, mobile app	Customer
API	Simplified interface for interacting with the backend	Waiter
Server	The backend where the processing happens	Kitchen

API Types

Medium

While this courses focuses on Web APIs, this term can apply to a broader range of interfaces:

• Hardware APIs - Interface for software to talk to hardware.
• Software Library APIs - Interface for directly consuming code from another code base.
• Web APIs - Interface for communicating across code based over a network.

Multiple API types may be used to achieve a task. For example, uploading a photo to Instagram makes use of:

1. Hardware API for tha app to talk to your camera.
2. Software library API for the image to be processed with filters.
3. Web API for sending your image to Instagram’s servers.

Architectures

There is more than one way to build and consume APIs, such as:

• REST (Representational State Transfer)
• GraphQL
• WebSockets
• webhooks
• SOAP (Simple Object Access Protocol)
• gRPC (Google Remote Procedure Call)
• MQTT (MQ Telemetry Transport)

This course will focus on REST APIs since this is the most widely adopted API architecture. Some traits of REST APIs include not storing session state between requests, the ability to cache, and the ability to send and receive various data types.

Access

APIs also vary in the scope of who can access them:

• Public APIs (aka Open APIs) - consumed by anyone who discovers the API.
• Private APIs - consumed only within an org and not made public.
• Partner APIs - consumed between one or more orgs that have an established relationship.

The API we will use in this course will be a Public, REST, Web API.