Constraint Programming is an approach for modeling and solving combina-
torial problems that has proven successful in many applications. It builds on
techniques developed in Artificial Intelligence, Logic Programming, and Op-
erations Research. Key techniques are constraint propagation and heuristic
search.
Constraint Programming is based on an abstraction that decomposes a
problem solver into a reusable constraint engine and a declarative program
modeling the problem. The constraint engine implements the required prop-
agation and search algorithms. It can be realized as a library for a general
purpose programming language (e.g. C++), as an extension of an existing
language (e.g. Prolog), or as a system with its own dedicated language.
The present book is concerned with the architecture and implementation
of constraint engines. It presents a new, concurrent architecture that is far
superior to the sequential architecture underlying Prolog. The new architec-
ture is based on concurrent search with copying and recomputation rather
than sequential search with trailing and backtracking. One advantage of the
concurrent approach is that it accommodates any search strategy. Further-
more, it considerably simplifies the implementation of constraint propagation
algorithms since it eliminates the need to account for trailing and backtrack-
ing.