1. A method of processing a set of documents for generating a facts database, comprising: at a system having one or more processors and memory storing one or more modules to be executed by the one or more processors: accessing a source document from a document host; extracting one or more facts from the source document; identifying a set of linking documents that have one or more links to the source document, wherein a respective link contains anchor text; generating a set of candidate labels from the anchor text of the linking documents, a respective candidate label of the set of candidate labels comprising text extracted from the anchor text in the one or more links to the source document in the set of linking documents; selecting a respective candidate label from the set of candidate labels as a unifying subject of the one or more facts extracted from the source document; and storing in the facts database an information set distinct from the source document, wherein the information set includes the unifying subject, one or more entries corresponding to the one or more facts extracted from the source document, and source document information for the one or more facts corresponding to the one or more entries.