Oracle Text indexes text by converting all words into tokens. The general structure of an Oracle Text CONTEXT index is an inverted index where each token contains the list of documents (rows) that contain that token.
For example, after a single initial indexing operation, the word DOG might have an entry as follows:
This means that the word DOG is contained in the rows that store documents one, three, and five.
Merged Word and Theme Index
By default in English and French, Oracle Text indexes theme information with word information. You can query theme information with the ABOUT operator. You can optionally enable and disable theme indexing.
"Creating Preferences " to learn more about indexing theme information