One main difference between Qlik Sense and many other database viewers and online analytical processing tools (OLAP systems), is that in Qlik Sense, you do not need to predefine any hierarchies in the input data. The unique internal logic of Qlik Sense gives you the complete freedom to access any field as a full dimension in any order you like.
For most purposes, the built-in functionality is fully satisfactory, but in some situations, a predefined hierarchy can help you to display data more efficiently. In Qlik Sense, you can achieve this by defining hierarchic groups of fields as drill-down dimensions.
Any fields or calculated dimensions can be grouped together.