Hi Vinay,
You can always use SI_ANCESTOR=23 clause in Query builder where condition in order to get the objects underneath which is the id for the Public folder. keep in mind that SI_ ANCESTOR is an unindexed column by using which you may experience performance issues in large deployments with more BI content.
for extraction of absolute logical path, you should always go for a SDK code. this is because all the objects in path hierarchy are stored in the same table with parent-child relationship. you cannot use recursive calls in query builder as well as sub queries.
Regards
Mani