Aside from the question of my you want to build your own, rather than
buying an off-the-shelf solution (we have one, too) -- why Oracle? A text
search engine will give much better performance and have many more
text-oriented features than Oracle or another RDBMS. Search engines are a
kind of database, of course, but one that is oriented toward text, rather
than fielded data (which some of them also support).
Nick