The two languages combined are sufficient to write a complete application. Nail and Glue code both compile into the target language IGlue. The Nail compiler uses variants of the magic sets algorithm, and supports well-founded models. Static optimization is performed by the Glue compiler using techniques that include peephole methods and data flow analysis. The IGlue code is executed by the IGlue interpreter, which features a run-time adaptive optimizer.
References are a little dated.
Design and implementation of the glue-nail database system. Doc 186 Computer Science Press - Ullman, Database et al. A deductive database system - Phipps, Derr et al. Doc 35 Design overview of the NAIL - Morris, Ullman et al. Yet Another Window on NAIL - Morris, Naughton et al.