5. The method of claim 4 , wherein identifying one or more text strings from the plurality of data sources that include one or more of the topics associated with the keyword included in the search query comprises: searching the reverse index of text strings using the one or more topics associated with the keyword included in the search query; and identifying text strings related to one or more topics associated with the keyword included in the search query.
4. The method of claim 1 , further comprising: maintaining, in a database, a reverse index of text strings that relates each topic to a text string from the plurality of data sources in which the topic occurred.