Sequential composition of schema mappings

A method for generating a schema mapping. A provided mapping M12 relates schema S1 to schema S2. A provided mapping M23 relates schema S2 to schema S3. A mapping M13 is generated from schema S1 to schema S3 as a composition of mappings M12 and M23. Mappings M12, M23, and M13 are each expressed in terms of at least one second-order nested tuple-generating dependency (SO nested tgd). Mapping M13 does not expressly recite any element of schema S2. At least one schema of the schemas S1 and S2 may comprise at least one complex type expression nested inside another complex type expression. Mapping M13 may define the composition of the mappings M12 and M23 with respect to a relationship semantics or a transformation semantics.