7. A non-transitory computer readable storage medium storing one or more computer programs executed by a computerized server system, the one or more computer programs comprising instructions to generate a facts database, the instructions including: instructions to access a source document from a document host; instructions to extract one or more facts from the source document; instructions to identify a set of linking documents that have one or more links to the source document, wherein a respective link contains anchor text; instructions to 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; instructions to 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 instructions to 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.
7. A non-transitory computer readable storage medium storing one or more computer programs executed by a computerized server system, the one or more computer programs comprising instructions to generate a facts database, the instructions including: instructions to access a source document from a document host; instructions to extract one or more facts from the source document; instructions to identify a set of linking documents that have one or more links to the source document, wherein a respective link contains anchor text; instructions to 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; instructions to 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 instructions to 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. 9. The computer readable storage medium of claim 7 , wherein the instructions to select a respective candidate label as a unifying subject comprise 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 label is associated with a respective frequency vector having a shortest distance to the centroid vector.