A method for generating a schema mapping. A provided mapping M.sub.12 relates schema S.sub.1 to schema S.sub.2. A provided mapping M.sub.23 relates schema S.sub.2 to schema S.sub.3. A mapping M.sub.13 is generated from schema S.sub.1 to schema S.sub.3 as a composition of mappings M.sub.12 and M.sub.23. Mappings M.sub.12, M.sub.23, and M.sub.13 are each expressed in terms of at least one second-order nested tuple-generating dependency (SO nested tgd). Mapping M.sub.13 does not expressly recite any element of schema S.sub.2. At least one schema of the schemas S.sub.1 and S.sub.2 may comprise at least one complex type expression nested inside another complex type expression. Mapping M.sub.13 may define the composition of the mappings M.sub.12 and M.sub.23 with respect to a relationship semantics or a transformation semantics.