Your comments

The pluging reservation fix some problems (mail remainder, free / busy material, late return reservation)

but some improvement can be done:

  1. Reservation can be deleted : The bit 'IsDeleted' should be added and delete reservation can be done only by purge right
  2. Prohibit reservations delete all reservation, so this button should be enable only on purge right
  3. The pluggin reservation allow a return valdation but this validation can be by passed
  4. Create / modify / delete (isdeleted) reservation can be done by maker reservation right if the reservation is not started
  5. Modify / delete (isdeleted) / Validate reservation can be done only by modify / delete right
  6. May be a button to confirm that the reservation is started (object is given to the user)