Cadence verification tools history

[camelot]

Sorry if I annoy you with this strange questions but someone could
explain to me what are the real differences among this verification
Cadence tools: Dracula, Vampire, Diva and Assura.
I took a look at the Cadence site and even on Vampire, I'm was not able
to find any useful information.
A little of history is always useful to better understand what rules
this environment.

Thank,

Camelot

 

[camelot]

Thank yoy Bernd,
your information have been very useful.

Cemelot