1. A method for generating an ontology, comprising: selecting, by a processing device, a tag in a tag cloud; searching, by the processing device, an online encyclopedia for content corresponding to the selected tag; determining, by the processing device, at least one category to which the content belongs in the online encyclopedia in response to finding the content corresponding to the selected tag in the online encyclopedia; and adding, by the processing device, a class to the ontology corresponding to the at least one category of the content in the online encyclopedia.