Parties identify themselves.
"Alice, do you marry Bob?"
Possible answers: Yes/No/No Response
if yes, this is the point of no return. Local commitment.
"Bob, do you marry Alice?"
Possible answers: Yes/No/No Reponse
if no, Alice is off the hook. This is an atomic priniple.
if yes, priest says "By the power invested in me by the State of California, I pronounce you husband and wife"
this is commitment, and this passes the ACID test.