I've searched the web and found out that "osmosis" is the key. also, this blog http://learnosm.org/en/osm-data/osmosis/ gave me a huge hint and i made it to extract POI tag by tag (by the way, i am using windwos)
as you know, there are hundreds of tags in OSM and going through all the tags and paste that in the command window is not feasible. so, instead of writing "amenity.school", i used "amenity.*"
of course, it doesn't seem to work. You have any suggestions?