Source : Free On-Line Dictionary of Computing

REGTRAL
     
        Mentioned in Attribute Grammars, LNCS 323, p.108.
     
        Relational Language.  Clark & Gregory.  First parallel logic
        language to use the concept of committed choice.  Forerunner
        of PARLOG.  "A Relational Language for Parallel Programming",
        K.L. Clark et al, Proc ACM Conf on Functional Prog Langs and
        Comp Arch, pp.171-178, ACM 1981.