[1-7] Commercial Object-Oriented Systems for Prolog

LAP is an object-oriented system by Elsa. For more information, write
to Elsa Software, La Grange Dame Rose, 6 ave du Marechal Juin, 92366
Meudon-La-Foret Cedex, France, call +33 (1) 46 30 24 55, fax +33 (1)
46 30 55 26, or send email to elsa!lap@uunet.uu.net.

SPIRAL is an object oriented system by CRIL for Sun3 and Sun4 under
Unix. For more information, write to CRIL, Conception et Realisation,
Industriel de Logiciel, 146 bd de Valmy 92707, Colombes Cedex, France,
call +33 1 47 69 53 67, or fax +33 1 47 69 53 99.

Quintus Prolog (see [2-2]) has an object system documented in
   http://www.quintus.com/prolog/obj.html
and in Peter Schachte's home page,
   http://muse.cs.mu.oz.au/%7Epets/
Quintus objects are updateable data structures whose slots can contain
Prolog terms. (For increased efficiency, a slot can be constrained to
hold a specific C-style type.) Because the objects are updateable,
they offer and efficient alternative to storing modifiable data in the
Prolog database. 

See also LPA Prolog ++ in [2-2].