1. A method comprising: generating, by a computing device and based at least in part on information about an input item, a context of the input item; comparing, by the computing device, the context of the input item to respective contexts of a plurality of other items to determine respective levels of similarity between the input item and each of the plurality of other items; and annotating the input item with information derived from at least one of the plurality of other items based at least in part on the respective levels of similarity between the input item and each of the plurality of other items.