DomainKeys VS. DKIM (DomainKeys Identified Mail)

DomainKeys VS. DKIM (DomainKeys Identified Mail)

Could someone please explain to me the difference between DomainKeys and  DKIM (DomainKeys Identified Mail)? I know what they are, but they sound like the same thing to me. Do you need only one on or both of them on? (We have DKIM on, and it's working well.) Can you even have both of them on?
Thanks,
Noble Obodum
Head Webmaster, AOK
nobodum@theaoks.gq
webmaster@theaoks.gq