Table Keys : Surrogate , Replacement , Alternate , Primary and foreign key in AX 2012

Dear All,

I read msdn documents but not properly understand why "Surrogate , Alternate and Replacement key" is introduced in AX 2012.
Can you please explain me with proper real scenario of"Surrogate , Alternate and Replacement keys". How it's work practically in table level. What is the advantage of those keys?

Thanks!

Arpan Sen