The connection must have a meaning.
If we only know that a subject is connected to an object, then this connection is meaningless.
A strange example would be the 'has nothing to do with' relation. This relation is however meaningful.
The relation is only a connection from a subject to an object, it does not imply any connection from object to subject.
There is no notion of an inverse relation.
Assume we have a family with a grandparent, a parent and a child.
The following relations hold: