15. A computer readable storage medium storing one or more programs configured for execution by a computer, the one or more programs comprising instructions to: identify a first set of documents based on a first model and a first set of features, wherein the first model includes a first set of rules specifying at least one combination of features from the first set of features that are sufficient for identifying a document referring to an entity, each document of the first set of documents comprising a sufficient number of features in common with the first set of features to identify a document referring to the entity according to the first model; determine a second model based on the features of the first set of documents, wherein the second model includes a second set of rules specifying at least one combination of features from the first set of documents that are sufficient for identifying a document referring to the entity; identify a second set of documents based on the second model and the first set of features, each document of the second set of documents comprising a sufficient number of features in common with the first set of features to identify a document referring to the entity according to the second model; identify a second set of features based on the second set of documents; determine if the second set of features are associated with the entity; and responsive to determining that the second set of features are associated with the entity, identifying a third set of documents based on a third model and the second set of features, each of the third set of documents comprising a sufficient number of features in common with the second set of features to identify a document referring to the entity according to the third model.
15. A computer readable storage medium storing one or more programs configured for execution by a computer, the one or more programs comprising instructions to: identify a first set of documents based on a first model and a first set of features, wherein the first model includes a first set of rules specifying at least one combination of features from the first set of features that are sufficient for identifying a document referring to an entity, each document of the first set of documents comprising a sufficient number of features in common with the first set of features to identify a document referring to the entity according to the first model; determine a second model based on the features of the first set of documents, wherein the second model includes a second set of rules specifying at least one combination of features from the first set of documents that are sufficient for identifying a document referring to the entity; identify a second set of documents based on the second model and the first set of features, each document of the second set of documents comprising a sufficient number of features in common with the first set of features to identify a document referring to the entity according to the second model; identify a second set of features based on the second set of documents; determine if the second set of features are associated with the entity; and responsive to determining that the second set of features are associated with the entity, identifying a third set of documents based on a third model and the second set of features, each of the third set of documents comprising a sufficient number of features in common with the second set of features to identify a document referring to the entity according to the third model. 27. The computer readable storage medium of claim 15 , wherein the first set of features comprises at least a first feature and a second feature, and wherein the second model specifies that an occurrence of the first feature is sufficient to identify a document referring to the entity.