Difference between Prolog and Expert Systems

[Marc Colinet]

Hello Everybody !

I wonder what kind of differences exist between Prolog and expert systems. 
Willing to implement a module specialised in decision taking, I wonder what 
is the most convenient for such a functionality. By decision taking I mean 
make a diagnostic, control a system and plan a mission.
Could you explain me the difference between them and the choice I should do 
for that ?

Thank you.
Cheers, Marc.