7. The method of claim 1 , further comprising: generating, by the one or more processors, the temporal link between the first keyword and the third keyword based on comparing the frequency of co-occurrence of the first keyword and the third keyword on the online documents with the historical frequency of co-occurrence.
1. A method of temporal content selection via a computer network, comprising: receiving, by one or more processors, responsive to a search query input into a search engine, a request for a content item to be displayed alongside search results, the request associated with a first keyword corresponding to the search query; parsing, by the one or more processors, a data structure storing historically linked keywords to select a second keyword linked to the first keyword via a historical link, the historical link generated based on a frequency of co-occurrence of the first keyword and the second keyword in historical content; selecting, by the one or more processors, based on the second keyword, a first content item for display alongside the first search results; receiving, by the one or more processors, a second request for a content item to be displayed alongside second search results, the second request associated with the first keyword; parsing, by the one or more processors, a second data structure storing temporally linked keywords to select a third keyword temporally linked to the first keyword in the second data structure based on a frequency of co-occurrence of the first keyword and the third keyword in online documents published within a temporal threshold satisfying a frequency of co-occurrence threshold, wherein the temporal link between the first keyword and the third keyword is based on comparing the frequency of co-occurrence of the first keyword and the third keyword in the online documents with a historical frequency of co-occurrence of the first keyword and the third keyword; identifying, by the one or more processors, a plurality of content items matching the third keyword; determining, by the one or more processors, that a content provider of a second content item of the plurality of content items provided an indication to use temporal links for content selection; and selecting, by the one or more processors based on the indication, the second content item as a candidate for display alongside the second search results.