about rfid reader and rfid tag

[Nice]

i got a little bit confuses about: all the rfid reader whether can read all frequency(LF,HF,VHF AND UHF) of rfid tag ? what is the classification of rfid reader? frequency ? there are three type rfid tag : active, semi-active and passive. then the rfid tag still can classification : low frequency tag, high frequency tag, ultra high frequency tag ? and i also see some website say about :inductively coupled RFID tags,Capacitively coupled tags. can i know how to classification about reader and tag? thanks..