1. A method for candidate answer generation in a question answering system, comprising: receiving at least one document or passage responsive to a search of an information source, the search being implemented based on a query formulated from a natural language query; receiving provenance information for the at least one document or passage; searching a semi-structured source of information based on the provenance information; retrieving a substructure corresponding to the at least one document or passage from the semi-structured source of information; and returning the substructure as a candidate answer to the natural language query.