SNMP v1, v2, v3 are they compatible?

Dear IETF People,

I am working on my Masters degree at UWC. I was hoping
someone would be able to clarify whether the different
versions of SNMP are really not compatible or whether I have
mssed something in my search.

Thanking you and awaiting your reply in anticipation.

Regards
Tania Paulse (taniap(_at_)uwc(_dot_)ac(_dot_)za)
University of the Western Cape