multi-relation indices

Hi ,

This is first time I am trying to do development on POSTGRES.
I am trying to build multi-relational indices. So that when user enters 
keyword he will get in which relation in which tuple this keyword occured.
This is also known as inverted indices. I am thinking of adding Index at 
database level which will kepp track of all keywords. Another approach 
is to create a dummy table which will store information of all words in 
database. And add index on this tacle. Can any one guide me regarding 
how feasiable these method are? And if feasiable which one is better?

Regard's,
~Ajay