The paper on microKanren [1] is imho the most approachable piece outside the "reasoned schemer" [2]. The thesis on which it is based is also interesting but is a thicker beast. Looking at stuff from the clojure world (clojure.core.logic and this talk [3]) is also interesting imho, especially from a dev perspective. From this point of view I found this talk [4] to be especially enlightening in how to build a database / query engine and concrete applications of MiniKanren / datalog.