Datomic

• A commercial immutable database. Facts are never overwritten, only added, so you can query the database as of any past moment in time.
• Data is stored as datoms, entity-attribute-value triples, queried in Datalog directly:

[:find ?name
 :where [?p :person/age ?a]
        [(>= ?a 18)]
        [?p :person/name ?name]]

• Shared logic variables join the clauses: here ?p links a person’s age to their name, exactly as a shared variable joins atoms in a Datamog rule body.