Like MS Outlook we should have the possibility for members to set the option participation unsure.
If a member is assigned by Webmaster or leader of the event this option shouled be set automatically. The assigned member needs to confirm with yes,no or unsure. Therfore we need a additional flag in database table of the event role. It could be a numeric field with value dafault 0 for not confirmed by member, 1 confirmed by member. Also a new timestamp column for confirmation from user should be implemented in table.