Acts_as_taggable

Hello All,

I have a table for which i need to tag and i am applying
acts_as_taggable for that

I have a table called localities and I created a table called tags
and tags_localities ,Now my requirement is i need to create new tags
and i should be able to add sub tags to the new tags

So its basically applying Tagging on tags agian

can any one give me a idea of how can i do this

Thanks
Jagan