Additional modeling aspects
Besides hierarchical dependencies, there is a wide choice of other ways to introduce predefined collections. One was is to associate certain properties with a member and group members by properties. This normally requires an additional index to ensure efficient processing.
Some of the properties, or even some of the member names may be evenly distributed, creating a periodical pattern. The best example is time related dimensions which usually display periodicity: particular quarters and months tend to occur every year, particular hours occur once a day, minutes - once an hour, etc.