28. A system comprising: one or more computer devices to: receive labels for a first document from a plurality of different users; detect a first link between the first document and a second document, based on at least one of the received labels matching a label associated with the second document; detect a second link between the first document and a third document, based on at least one of the received labels and a label associated with the third document being sibling labels; assign a rank score to the first document based on the first link and based on the second link, where the first link contributes more to the rank score than the second link, and where the rank score is further based on a quantity of the plurality of different users; detect a third link between the second document and a fourth document, based on the second document and the fourth document sharing a same label that is not shared by the first document; and modify the rank score of the first document based on the detected third link.
28. A system comprising: one or more computer devices to: receive labels for a first document from a plurality of different users; detect a first link between the first document and a second document, based on at least one of the received labels matching a label associated with the second document; detect a second link between the first document and a third document, based on at least one of the received labels and a label associated with the third document being sibling labels; assign a rank score to the first document based on the first link and based on the second link, where the first link contributes more to the rank score than the second link, and where the rank score is further based on a quantity of the plurality of different users; detect a third link between the second document and a fourth document, based on the second document and the fourth document sharing a same label that is not shared by the first document; and modify the rank score of the first document based on the detected third link. 29. The system of claim 28 , were the rank score is further based on a quantity of discrete labels received for the first document from the plurality of different users.