Natural language interfaces (NLIs) have been the "holy grail" of natural language understating and human-computer interaction for decades (Woods et al., 1972;Codd, 1974;Hendrix et al., 1978;Zettlemoyer and Collins, 2005).
early attempts in building NLIs to databases did not achieve the expected success due to limitations in language understanding capability, among other reasons (Androutsopoulos et al., 1995;Jones and Galliers, 1995).