What is an API?

We are connected with the world, and with each other, like never before. You can purchase goods, post feeds, upload pictures, or make a restaurant reservation via a mobile device or your computer. All that connectivity is enabled by the use of so-called APIs. According to Wikipedia (https://en.wikipedia.org/wiki/Application_programming_interface), an API is a set of subroutines, definitions, protocols, and tools that can be utilized for building applications. It's a collection of building blocks that abstract the underlying implementation of a technology by only exposing specific objects or actions a developer can perform, and simplifies programming by doing so. In the example of a Qlik Sense API, the querying of the underlying technology, the Qlik data engine, is abstracted by the use of predefined calculation and aggregation expressions (sum, avg, count...