CLIPS was not a direct OPS5 replacement. CLIPS was replacing the usage of ART (AUTOMATED REASONING TOOL) at NASA. ART was a proprietary, large and extremely exp

CLIPS was not a direct OPS5 replacement. CLIPS was replacing the usage of ART (AUTOMATED REASONING TOOL) at NASA. ART was a proprietary, large and extremely expensive expert system development tool written in Lisp, which required workstation class systems. ART had a rule system influenced by OPS5. There were/are also cheaper versions of OPS5 itself written in Lisp.