When you insert the Transfer records in my example, you indicate that they are "edges/relationships" between "Account" node records. The system interprets the values in those records implicitly as foreign keys to the Account records. This is what I mean by "predefined joins" in my example. When you ingest your relationship records, you predefine a join to the system and the GDBMS uses those Transfer records to join node records.

Hope this helps.

in gdbms, there is the concept of "predefined joins" where you define a relationship edge that directly connects 2 nodes, i don't know how these guys do it, but at least in neo4j that's the concept

edit: just saw their blog, they ask you to define a "rel table" and that has to define all the joins and they load it from there