In interactive dispatching systems humans and computer cooperatively modify problem data and schedule using different problem knowledge and solution methods:
An interactive dispatching system allows these specialised actors to concurrently modify problem data and solution. Efficient transaction control schemes must be applied to ensure data consistency. As the computer continuously tries to optimise the schedule, it must not get an exclusive lock on data records. Otherwise, dispatchers would not be able to modify the locked data records. An optimistic locking scheme can be applied in order to prevent that changes made by one actor conflict with changes made by another actor. Optimistic locking does not lock data records when they are read, and proceeds on the assumption that the data records being updated will not be changed. To ensure data consistency, the optimistic locking scheme proposed involves reading a Transaction Control Number (TCN) along with each data record representing an order or a tour. When the schedule is changed by the dispatchers or the computer, the TCNs of the respective order and tour are written back to the database when the record is updated. A pre-update trigger checks the value of the updated TCNs against those held in the database. If the TCNs do not match, the transaction is rejected. With each successful update, the TCNs of the order and tour are incremented. Furthermore, if dispatchers MFMS change attributes of data records concerning orders or tours, the TCNs are also incremented. The increment of the TCNs ensures that no other transaction that holds the same TCN will be able to modify the record.