The design of an appropriate conceptual database scheme is one of the most difficult tasks in usual database applications especially the design of a common global database scheme for many different user groups requires a great amount of effort and skill because the desired scheme should fit a great variety of requirements and expectations are separately collected and specified as views that are subsequently integrated into a global scheme, supporting all those different views. in this paper we carefully develop a formal model clarifying many notions and concepts, related to the view integration method this formal model serves as a theoretical basis of our integration approach that uses equivalence preserving local scheme transformations as the main integration operations.