Form documents or screen forms bring essential information on the data manipulated by an organization. They can be considered as different but often overlapping views of its whole data. This paper presents a non-destructive approach of their integration. The main idea of our approach is to keep the original views intact and to specify constraints between overlapping structures. For reasoning over constraints, we provide a set of inference rules that allows not only to infer implied constraints but also to detect conflicts. These reasoning rules are proved to be sound and complete. Although the form-based views are hierarchical structures, our constraints and reasoning rules can also be used in non-hierarchical data models.