Here is my thought on your query:
In a graph data model such as Reltio, A relationship defines a link between two physical entities/nodes. Link in turn represents a real world association between two real world objects. e.g., Two persons in real work can share a joint account hence both individual are nodes and having a common account is the link aka relationship. Similarly An Org and an Employee are two node which can share employer to employee relationship. Hope this helps
------------------------------
Ashish Rawat
Sr. Manager
Fresh Gravity
Bangalore
------------------------------