A method and system for processing a schema mapping M from a source schema S to a target schema T by executing program code on a processor of a computer system. A schema mapping M′ from T to S is determined via processing the schema mapping M. The schema mapping M includes at least one constraint σ. Each constraint σ consists of a source-to-target tuple-generating dependencies (s-t tgd). The schema mapping M′ includes at least one constraint σ′. Each constraint σ′ consists of a disjunctive tgd with constants and inequalities among the constants. The schema mapping M′ is stored in at least one computer usable storage device of the computer system and/or is outputted in at least one output device of the computer system.