Electronic B2B marketplaces bring together many online suppliers and buyers, each of which can potentially use his own format to represent the products in his product catalog. The marketplaces have to perform non-trivial mappings of these catalogs. In this paper, we analyze the problems which occur during the integration, taking several leading XML-based standards as an example. We advocate a three-layer product integration framework to resolve the difficulties in overcoming these problems with a direct one-layer integration. In this paper, we focus on the first two layers: the XML-based syntax layer and the data models layer expressed in RDF. The approach operates in three main steps. First, we create an RDF data model from the XML catalog, which eliminates all syntactical peculiarities of the catalog. Second, the catalog is translated from the source model to the RDF model of the target catalog. Finally, the transformation from RDF to XML restores all syntactical regulations required...