Some columns in a list often contain data that in some way is hierarchically superordinate to values in other columns.
The Airline column contains the names of airlines. The remaining columns contain detailed data for the flights for each airline, such as flight number, flight date, and price. You can therefore view the Airline column as superordinate to the other columns.
You can highlight the hierarchical structure within a list by displaying the list as a hierarchy (see Showing and Hiding Hierarchies).
The following list outlines the most important properties of a hierarchy:
The hierarchically superordinate columns are called hierarchy columns. You can set any number of columns as hierarchy columns. All hierarchy columns are then merged into one column and displayed in the first column of the list.
The data that is hierarchically subordinate can be hidden or shown.