Abstract. The interoperability of heterogeneous data sources is an important issue in many applications such as mediation systems or web-based systems. In these systems, each data source exports a schema and each application defines a target schema representing its needs. The way instances of the target schema are derived from the sources is described through mappings. Generating such mappings is a difficult task, especially when the schemas are semi structured. In this paper, we propose an approach for mapping generation in an XML context; the basic idea is to decompose the target schema into subtrees and to find mappings, called partial mappings, for each of them; the mappings for the whole target schema are then produced by combining the partial mappings and checking that the structure of the target schema is preserved. We also present a tool supporting our approach and some experimental results.