5. The method of claim 1 , maintaining, in a database, a reverse index of text strings that relates each topic identifier to a text string from the plurality of data sources in which the topics identifier occurred.
6. The method of claim 5 , wherein identifying text strings from the plurality of data sources that include topics associated with the identified one or more topic identifiers comprises searching the reverse index of text strings using the one or more identified topic identifiers to identify text strings in which the identified one or more topic identifies occurs.