Introduction to APIs

Back to API Design
Arjit Sharma
02 Mins

What is an API ?

API ( Application Programming Interface ) is an intermediatory that lets software components talk to each other.

It started with IBM’s release of CICS , which allowed different programs to communicate with each other and then later with UNIX’s system calls(api) became more mainstream.

What is an API Endpoint?

An API endpoint is simply a specific location on a server where your app sends a request and expects a response.

URI vs URL vs URN

  • URI ( Uniform Resource Identifier ) is general term for anything that identifies a resource.

  • URL ( Uniform Resource Locator ) is a type of URI that specifies location of resource on internet. It identifies “where”.

    Example - https://www.csprimer.in/page.html

  • URN ( Uniform Resource Name ) is a type of URI that identifies a resource by name instead of location. It identifies “what” .

    Example - urn:isbn:0451450523

Benefits of APIs

  1. Hiding complexity - You dont need to learn how Google Maps work, just ask what you want.
  2. Improved Modularity - Teams can build parts of system independently.
  3. Efficient development - Use API’s instead of re-inventing the wheel. Example - just use Stripe for payment

Types of APIs

  1. Public APIs - Free to access by consumers. Example: Google Maps API lets apps show locations or directions.
  2. Private APIs - Used within the organization. Example: A bank’s internal API for checking customer balances between systems.
  3. Partner APIs - Used between two strategic business partners. Example: Amazon shares APIs with delivery partners to track packages.
  4. Composite APIs - Bundle multiple requests into one. Example: Purchasing an item on Amazon involves adding product to cart, then checkout and then make payment. Combine all in one.

Business-Side of APIs

At the end of the day, APIs are products, and are sold by companies. So lets look at some business terms -

  • SLI (Service Level Indicator) is quantitative measure of service being provided.

    👉 “How fast does the API respond?”

  • SLO (Service Level Objective) is target set for one or more SLI.

    👉 “We aim for 99.9% uptime and 200ms response time.”

  • SLA (Service Level Agreement) is contract between customer and provider.

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