Constraint Based Spatial and Temporal Reasoning

can be used in both cases. Having in mind the application of this module to really hard problems we have introduced: ffl the management of a set of constraints defined on two variables with very similar motivations of that discussed in [5] (Total Constraint). We make a distinction between a constraint and a constraint arc. The first one is the usual constraint, the second one represents the dynamically defined collection of constraints between two variables. Furthermore, when one considers a particular class of constraints it is possible to take advantage of the restriction and develop ad hoc representations that enable efficient management during constraint reasoning. For instance, in the case of bounded difference constraints [4] (x \Gamma y a) the constraint arc, if disjunctions are not allowed, can be defined using only two, possibly infinite, real values (b x \Gamma y<F38.