Physically-based modeling has been used in the past to support a variety of interactive modeling tasks including free-form surface design, mechanism design, constrained drawing, and interactive camera control. In these systems, the user interacts with the model by exerting virtual forces, to which the system responds subject to the active constraints. In the past, this kind of interaction has been applicable only to models that are governed by continuous parameters. In this paper we present an extension to mixed continuous /discrete models, emphasizing constrained layout problems that arise in architecture and other domains. When the object being dragged is blocked from further motion by geometric constraints, a local discrete search is triggered, during which transformations such as swapping of adjacent objects may be performed. The result of the search is a "nearby" state in which the target object has been moved in the indicated direction and in which all constraints are satisfied. ...

this paper to structural and syntactic methods does of course in no ways mean that we despise or reject the statistical approach to pattern recognition. Actually, the complementarity of these two families has already been extensively proved [24], attributed and stochastic grammars have been proposed [36, 58] and used in various applications [53, 55], probabilistic relaxation is often used in connection with structural matching [9], etc. But in this paper, we concentrate on the use of structural and syntactic pattern recognition methods when dealing with the analysis of graphics and line drawings. 2 Structural and syntactic methods in document and graphics analysis