I meant relational programming in the sense that William E. Byrd uses it, as something like a close cousin or a different way of looking at logical programming
miniKanren is being used for research in "relational" programming. That is, in writing programs that behave as mathematical relations rather than mathematical functions. For example, in Scheme the append function can append two lists, returning a new list: the function call (append '(a b c) '(d e)) returns the list (a b c d e). We can, however, also treat append as a three-place relation rather than as a two-argument function. The call (appendo '(a b c) '(d e) Z) would then associate the logic variable Z with the list (a b c d e). Of course things get more interesting when we place logic variables in other positions. The call (appendo X '(d e) '(a b c d e)) associates X with (a b c), while the call (appendo X Y '(a b c d e)) associates X and Y with pairs of lists that, when appended, are equal to (a b c d e). For example X = (a b) and Y = (c d e) are one such pair of values. We can also write (appendo X Y Z), which will produce infinitely many triples of lists X, Y, and Z such that appending X to Y produces Z.
It's called SQL, and it's pretty big and you can get paid a lot for being good at it.