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). The engine can read those commands and returns the corresponding aggregated result.

To speak plainly, the API is a messenger...