The following features should be provided:

• Do not change the timeslot when replanning
  Talks have a “publishedTimeslot” and a “publishedRoom”
• Popularity changes effect on talks to big rooms
• Last-minute speaker unavailability (or other hard constraint input changes): Given additional speaker unavailability preventing that speaker to give the published talk at the original timeslot, do minimal changes to get a feasible schedule.

To implement these, optaplanner will allow this through these 2 constraints:

• If publishedRoom is filled in, there’s a very soft constraint not to change that
  Very soft to avoid unneeded disruption
• If publishedTimeslot is filled in, there a medium constraint not to change that
  So it only gets changed if we need it to fix any hard constraint (such as new speaker unavailability)