Relations in the relational databases are handled by the joins between the tables,These can be managed in two ways :either in a permanent declarative fashion by the use of foreign
keys, or in a temporary fashion by ad-hoc joins in our queries

Hierarchical data on the other hand, is often modelled with self joins

Whereas in Graph Databases the relationships  physically exist on disk and they are named, directed, and can be themselves decorated with properties This means if you chose to, you could look at the relationships on disk and see how they “join” entities. Relationships are therefore first-class entities in a graph database and are semantically far stronger than those implied relationships reified at runtime in a relational store.