Keyword usage score based on frequency impulse and frequency weight

A computer-readable medium encoded with instructions for controlling a computing device to assess keyword usage, by a method comprising:

• providing a search log for each of a plurality of periods, a search log of a period indicating search requests submitted to a search engine service during that period, each search request including keywords;
• calculating a frequency impulse score for a keyword, the frequency impulse score indicating a change in frequency of the keyword occurring in search requests of a search log for a recent period;
• calculating a frequency weight for the keyword, the frequency weight indicating a measure of the frequency of the keyword occurring in search requests of the search log for the recent period;
• and
• multiplying the frequency impulse score and frequency weight of the keyword to give a recent usage score of the keyword.

A computing system for ranking documents, comprising:

• a data store that indicates frequency of keywords;
• a component that calculates a recent usage score for a keyword by combining a frequency impulse score for the keyword and a frequency weight of the keyword, the frequency impulse score indicating a recent change in frequency of the keyword and the frequency weight indicating a recent measure of the frequency of the keyword;
• and
• a component that ranks documents of a search result of a search request based at least in part on the recent usage score of the keyword.