Need info on taxonomic keys

[Mike]

I'm doing a bio lab and the teacher wanted us to write about the 
advantages/disadvantages of a dichotomous key, but i've had little luck at the 
local library.  If anyone can give me info about this type of key, along with 
other taxonomic keys, which he wants for comparison, it would be appreciated. 

Mike

PS--I need it before Monday the 29th, so if anyone knows please get back to 
me.  THanx