Source : Free On-Line Dictionary of Computing

OPS5
     
         A programming language for rule-based {production
        system}s.  A rule consists of pre-condition(s) and a resulting
        action.
     
        The system checks its working memory to see if there are rules
        whose pre-conditions are satisfied, if so, the action in one
        selected satisfied rule is executed.
     
        There is a {public domain} implementation of an OPS5
        {interpreter} written by Charles L. Forgy 
        in 1977.  It was first implemented in {Lisp} and later in
        {BLISS}.  It was also ported to {Common Lisp} by George Wood
        and Jim Kowalski.
     
        {CLIPS} is a language for writing {expert system}s, with some
        of the capabilities of OPS5.
     
        See also {C5}, {OPS83}, {OPS4}, {OPS5+}, {OPS83}.
     
        Inference Engine Tech, Cambridge MA.
     
        {An OPS5 interpreter in Common LISP
        (ftp://ftp.wustl.edu/mirrors/Unix-c/languages/ops5)}.
     
        {A version by Mark Kantrowitz
        (ftp://ftp.cs.cmu.edu/afs/cs.cmu.edu/user/mkant/Public/Lisp/)}.
        .
     
        ["Programming Expert Systems in OPS5", L. Brownston et al, A-W
        1985].
     
        ["An OPS5 Primer", Sherman et al, comes with OPS5 for DOS].
     
        ["Rule-Based Programming in the Unix System", G.T. Vesonder,
        AT&T Tech J 67(1), 1988].
     
        (1995-08-18)