1. A computer-implemented method for corroborating a set of facts included in a fact repository, the method comprising: at a back end computer system including one or more processors and memory storing one or more programs, the one or more processors executing the one or more programs to perform the operations of: identifying a set of facts associated with an object, the set of facts having been previously extracted from multiple documents, each fact comprising an attribute-value pair, including a fact attribute type and a fact value, and wherein the object is associated with an entity having a name fact attribute type; receiving a first document not included in the multiple documents and a reference to the first document, said reference comprising user-viewable anchor text extracted from a second document; determining that the user-viewable anchor text matches the name of the entity associated with the object; determining that one or both of the name of the entity associated with the object or the user-viewable anchor text appears in the first document; and responsive to determining that the user-viewable anchor text matches the name of the entity associated with the object and that one or both of the name of the entity associated with the object or the user-viewable anchor text appears in the first document, corroborating the set of facts using the first document; the corroborating comprising: identifying one or more facts in the first document, each identified fact having an attribute-value pair; and comparing a respective attribute-value pair of the set of facts to an identified attribute-value pair in the first document; and updating the set of facts in accordance with the corroborating, wherein the updating includes one or both of storing an attribute-value pair from the first document in the set of facts in association with the object or adjusting a status of an attribute-value pair of the set of facts.