1. A method, performed by one or more server devices, the method comprising: identifying, by one or more processors of the one or more server devices, a set of second documents that each contains a link to a first document; determining, by one or more processors of the one or more server devices, a freshness attribute associated with each document of the set of second documents; assigning, by one or more processors of the one or more server devices, a freshness score to the first document based on the freshness attribute associated with each document of the set of second documents; and ranking, by one or more processors of the one or more server devices, the first document with respect to at least one other document based on the freshness score assigned to the first document.
3. The method of claim 1 , further comprising: determining that a document, in the set of second documents, is fresh when the document has been updated within a particular period of time relative to a current time; and determining that the document is not fresh when the document has not been updated within the particular period of time.