15. The method of claim 1 , further comprising: generating, by the computing device, a topic database for use in annotating input items, the topic database specifying a plurality of topics; constructing, by the computing device, a global descriptive context for each topic in the topic database; and ranking, by the computing device, each topic in the topic database by comparing the respective descriptive context for each of the topics to the descriptive context for the input item.
15. The method of claim 1 , further comprising: generating, by the computing device, a topic database for use in annotating input items, the topic database specifying a plurality of topics; constructing, by the computing device, a global descriptive context for each topic in the topic database; and ranking, by the computing device, each topic in the topic database by comparing the respective descriptive context for each of the topics to the descriptive context for the input item. 17. The method of claim 15 , wherein performing the normalization process includes conducting a topic query for the one or more topics in the topic database using a crowd-sourced information source, and updating the topic database based at least in part on the results of the topic query.