As always, it depends what you’re trying to do…
If you are looking at maintaining relationships between Things, probably the easiest way to look at it is to separate the entities from their relationships (i.e. model it as a digraph with nodes and edges - you could take a look at GitHub - bitwalker/libgraph: A graph data structure library for Elixir projects · GitHub for inspiration).
Other than that, looking up other entities by some kind of key is a pretty common approach. How that is implemented depends on what you are trying to achieve (in detail). For example, GitHub - lau/tzdata: tzdata for Elixir. Born from the Calendar library. · GitHub provides a timezone database for elixir - it builds the data and relationships in ets on startup (and periodically updates on a schedule when timezone databases update) and provides data back to consumers via lookups on the ets tables. Incidentally, it is building links between entities as part of the database build process to allow alias names for timezones.
