1. A system comprising: one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising: generating a score for each of a plurality of items, the generating comprising, for each item: obtaining a respective item-specific value of each of a plurality of indicators; determining a respective weight for the value of each of the plurality of indicators, wherein the respective weight for one or more of the plurality of indicators is derived from the value of the indicator; and generating the score for the item from the item-specific values, wherein generating the score comprises combining the item-specific values and weighting each item specific value by the respective weight for the value; and providing the score for each item to a ranking engine implemented on one or more computers, wherein the ranking engine ranks resources based, at least in part, on the scores for the items.