Abstract: A system and a method are disclosed for processing hierarchical data structures, for example, XML (extensible markup language) documents. A tree view shows a visual representation of the input schema and the output schema and visual representations of associations between nodes from the input schema and output schema. A grid view shows mapping statements configured to map the input hierarchical data structure conforming to the input schema to an output hierarchical data structure conforming to the output schema. The grid view and the tree view are synchronized such that modifications performed using any one view result in corresponding modifications being presented in the other view. Modifications to mapping statements are validated to determine if path expressions used in the mapping statements are valid in the modified mapping statements.