Sup guys

I'm kinda new around "stumblin" the wireless community, so I got some question.

What is the diff between parabolic antenna and a yagi?
I thought both are for long distance, but what's the diff?

and also, is the diff between parabolic 19db and 24 db big?
'coz the price diff is so big....

thats all 4 now....thanx in advance