Three Potential Types of API Platforms

I'm processing all my notes from the 2011 Glue Conference, which has been one of the most thought provoking events I've been to this year.

The best part of events like Gluecon is you get to hang with some really smart and extremely experienced people.

I'm working to understand a new perspective I was exposed to while listening to Mark Suster talk about the Cloud Computing: Challenges and Opportunities over the Next Five Years.

In his talk, he outlined three potential types of platforms:
  • Platform as a Service - Platform around core application or business as an API, allowing others to build businesses on top of, and make money.
  • Platform as an Extension - Platform around a core application that offers APIs as an extension for others to build on bringing value back to the core business.
  • Platform as a Trojan Horse - Platform that allows others to build on, taking the risk, and the core business benefits from any value created.
As I work my way through the hundreds of available APIS I will definitely be applying what I'm learning...

What is the motivation of each of these API platforms?