Defining Hierarchical Relations

If your document set consists of news articles, you can use a thesaurus to define a hierarchy of geographical terms. Consider the following that describes a geographical hierarchy for the state of California:

California
   NT Northern California
       NT San Francisco
       NT San Jose
   NT Central Valley
       NT Fresno
   NT Southern California
       NT Los Angeles

You can use the NT operator to expand a query on California:

'NT(California)'

is expanded to:

'California, Northern California, San Francisco, San Jose, Central Valley,
  Fresno, Southern California, Los Angeles'

The resulting hitlist shows all documents related to the state of California regions and cities.