1. A computer-implemented method for schema mapping and data transformation, the method comprising: loading a conceptual model, wherein the conceptual model contains at least one conceptual object; loading a source schema and a source instance; converting the source schema and the source instance into a source model; acquiring, from the user, at least one forward mapping usable to map at least a source attribute of the source model to a conceptual attribute of the conceptual model, wherein the forward mapping includes a mapping formula; loading a target schema and a target instance; converting the target schema and the target instance into a target model; and reverse mapping at least one of conceptual attributes of the conceptual model to a target attribute of the target model based on the forward mapping and the mapping formula.