Relationships
If you have already experience in RDB or graph databases, you are familiar with the concept of relations(or JOINS) or directed edges.
To provide relationships between stored documents in OrientDB, you can implement it in two ways:
You have always to consider that these two ways to connect your documents are always monodirectional or unidirectional, not bidirectional like in case of graph databases. You, as a designer of the database, are responsible to implement a bidirectional connection. Which means, in case of wanting a relation between two documents, you have to set links/references in both of these documents.