Muggleton, Stephen (1999). «Inductive Logic Programming: Issues, Results and the Challenge of Learning Language in Logic». Artificial Intelligence. 114: 283–296. doi:10.1016/s0004-3702(99)00067-3; here: Sect.2.1
Luc De Raedt. A Perspective on Inductive Logic Programming. The Workshop on Current and Future Trends in Logic Programming, Shakertown, to appear in Springer LNCS, 1999. CiteSeerX: 10.1.1.56.1790