Abstract

Schema mappings have been extensively studied in database research over the past decade - notably in the areas of data exchange and data integration. Recently, the notion of an information transfer order on schema mappings has been introduced to compare the amount of source information that is actually transferred by two mappings. In this paper, we present two new operators: the union and intersection of mappings. The union of two mappings allows us to describe the sum of all information transferred by several mappings. The intersection refers to the common part of information transferred by several mappings. As one of our main results we prove that there exists a large class of mappings (containing the class of source-to-target tuple-generating dependencies) that forms a complete lattice with respect to these two operators.