[help-GIFT] what is InvertedFileFeatureDescription.db ?

[Prawit Chaivong]

hi ,
i'm writing script for prepare database (like gift-add-collection.pl )
and i try to learn from gift-add-collection.pl . Then i found it 
extracted feature of each images
and create .db and .ADI file by "gift-generate-inverted-file" .that mean 
you must have url2fts.xml and InvertedFileFeatureDescription.db .
   url2fts.xml, i can make it but i have a problem with 
InvertedFileFeatureDescription.db ,
I know ,It come from "gift-write-feature-descs" script that received one 
argument .
And argument must be .ppm filename . This points make me confusing 
because i don't know
which file that i should put in script
   and last thing . I don't know ,what the 
InvertedFileFeatureDescription.db do ?
and wheater each  .ADI came from the same 
InvertedFileFeatureDescription.db or not ?
thank for help
Cheer
Prawir Chaivong