4. A server system for processing a set of documents for generating a facts database, comprising: one or more processors; memory storing one or more programs to be executed by the one or more processors, the one or more programs including instructions to: access a source document from a document host; extract one or more facts from the source document; identify a set of linking documents that have one or more links to the source document, wherein a respective link contains anchor text; and generate 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; select 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 store 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.
4. A server system for processing a set of documents for generating a facts database, comprising: one or more processors; memory storing one or more programs to be executed by the one or more processors, the one or more programs including instructions to: access a source document from a document host; extract one or more facts from the source document; identify a set of linking documents that have one or more links to the source document, wherein a respective link contains anchor text; and generate 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; select 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 store 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. 6. The system of claim 4 , wherein the instructions to select a respective candidate label as a unifying subject include instructions to: for each of the set of candidate labels: determine a set of frequencies of one or more substrings of the candidate label; and generate a frequency vector associated with the candidate label based on the set of frequencies; and determine a centroid vector based on the frequency vectors of the candidate labels, wherein the selected candidate label is associated with a respective frequency vector having a shortest distance to the centroid vector.