- J. Bowen and Dennis Bahler,
Conditional Existence of Variables in Generalized Constraint Networks,
*Proc. 9th Natl. Conf. on Artificial Intelligence (AAAI91),*
Anaheim, 1991, 215-220.

Classical constraint systems require that the set of variables which exist
in a problem be known *ab initio*.
However, there are some applications in which the existence
of certain variables is dependent on
conditions whose truth or falsity can only be determined dynamically.
In this paper, we show how this conditional existence of variables
can be handled in a mathematically well-founded fashion by viewing
a constraint network as a set of sentences in free logic.
Based on these ideas, we
have developed, implemented and applied, a constraint language
in which any
sentence in full first-order free logic, about a many-sorted
universe of discourse which subsumes the reals, is a well-formed constraint.

(504kb PDF)