Clojurians Log v2

A reference is a fact like any other. You can check if the fact is present.

[?person :person/children _]

Matches if ?person has a fact with attribute :person/children. Meaning ?person has a reference to a child. (You can elide trailing _, so you can write [?person :person/children]) Other way round:

[_ :person/children ?child]

Matches if ?child is referenced by some entity through the :person/children attribute.