27. An apparatus comprising: a desirability index including a plurality of desirability values, each desirability value being associated with a keyword, being determined according to a numerical value assigned to a selected item listing having the keyword based upon a sale format associated with the selected item listing, and indicating an accumulative frequency of the keyword being included in a first set of one or more item listings selected throughout a number of user transactions, the assigning of the numerical value comprising determining the numerical value based at least in part on whether the sale format associated with the selected item listing is a fixed price sale or a non-fixed price sale; at least one hardware processor to run a search engine, the search engine configured to identify a search result including a second set of one or more item listings in response to a query from a user device, each item listing including a plurality of keywords; and a lookup engine, executed by the at least one hardware processor, to access, for each item listing, the desirability index and obtain a desirability value for each keyword included in the item listing and to calculate a relevancy value for each item listing, the relevancy value being an accumulation of the desirability values for the keywords included in the item listing; wherein the search engine is configured to sort the item listings in the search result according to the relevancy values for the item listings and return the sorted item listings to the user device.
27. An apparatus comprising: a desirability index including a plurality of desirability values, each desirability value being associated with a keyword, being determined according to a numerical value assigned to a selected item listing having the keyword based upon a sale format associated with the selected item listing, and indicating an accumulative frequency of the keyword being included in a first set of one or more item listings selected throughout a number of user transactions, the assigning of the numerical value comprising determining the numerical value based at least in part on whether the sale format associated with the selected item listing is a fixed price sale or a non-fixed price sale; at least one hardware processor to run a search engine, the search engine configured to identify a search result including a second set of one or more item listings in response to a query from a user device, each item listing including a plurality of keywords; and a lookup engine, executed by the at least one hardware processor, to access, for each item listing, the desirability index and obtain a desirability value for each keyword included in the item listing and to calculate a relevancy value for each item listing, the relevancy value being an accumulation of the desirability values for the keywords included in the item listing; wherein the search engine is configured to sort the item listings in the search result according to the relevancy values for the item listings and return the sorted item listings to the user device. 29. The apparatus of claim 27 , wherein the lookup engine receives a specified temporal range from the user device.