12. The apparatus of claim 8 wherein the second set of semantic tags is obtained by applying a threshold to the output of the second classifier.
8. An apparatus comprising: a memory to store a plurality of existing content items; and a processor coupled to the memory, the processor to: provide a feature vector associated with a new content item to a first classifier, wherein the feature vector associated with the new content item includes a plurality of values representing one or more features extracted from content of the new content item, wherein the first classifier was trained using a plurality of features vectors of a plurality of existing content items to produce suggested semantic tags for respective existing content items; input a first set of semantic tags obtained from the first classifier for the new content item to a second classifier that was trained using input-output pairs, wherein an input of each input-output pair includes a subset of the suggested semantic tags that was previously produced by the first classifier and suggested to a first user for one of the respective existing content items, and wherein an output of the input-output pair includes one or more suggested semantic tags selected by the first user from the subset of the suggested semantic tags for the one of the respective existing content items; run the second classifier to obtain a second set of semantic tags for the new content item; and cause the second set of semantic tags to be presented to a second user as suggestions for the new content item.