13. A method, performed by one or more server devices, of determining the freshness of a first document, comprising: determining, by a processor of the one or more server devices, whether a freshness attribute is associated with the first document; identifying, by a processor of the one or more server devices and based on the determination, a set of second documents that each contains, or previously contained, a link to the first document; assigning, by a processor of the one or more server devices, a freshness score to the first document based on a freshness attribute associated with each document of the set of second documents or the freshness attribute associated with the first document, where the freshness attribute indicates when each document was last modified; and using, by a processor of the one or more server devices, the assigned freshness score as a basis for ranking the first document among a plurality of documents returned as results of an executed search.
13. A method, performed by one or more server devices, of determining the freshness of a first document, comprising: determining, by a processor of the one or more server devices, whether a freshness attribute is associated with the first document; identifying, by a processor of the one or more server devices and based on the determination, a set of second documents that each contains, or previously contained, a link to the first document; assigning, by a processor of the one or more server devices, a freshness score to the first document based on a freshness attribute associated with each document of the set of second documents or the freshness attribute associated with the first document, where the freshness attribute indicates when each document was last modified; and using, by a processor of the one or more server devices, the assigned freshness score as a basis for ranking the first document among a plurality of documents returned as results of an executed search. 20. The method of claim 13 , where assigning a freshness score to the first document further comprises: assigning a high freshness score to the first document if a majority of documents of the set of second documents have associated freshness attributes that indicate that the corresponding documents are fresh.