Preferred current flow in relay contacts?

Yet another relay question. In this document the moving and fixed part of a relay contact are named anode and cathode. This suggests that there's a preferred current flow through the contact in DC applications. Is this taken in consideration if both contact parts have different contact materials? For instance, if contacts are tungsten and silver-nickel for anode and cathode resp. (just an example, not necessarily realistic), are you supposed to have the anode more positive than the cathode?