Modifying existing timetables

[Vangelis Karafillidis]

Hello!

First of all, congratulations to Liviu Lalescu and Volker Dirr, for this excellent application!
In my country (Greece), most of the time, schools need to change their timetable during the school year, sometimes even up until April. This is due to the fact that the Greek Ministry of Education hires teachers even during the school year. So, schools need to modify their timetable from time to time. And it's not strange for a school to change its timetable even ten (10) or more times in the same school year. This results in a necessity for modifying an already existing timetable partially (i.e. as little as possible). On the other hand, FET is "fine tuned" for finding good solutions, for the overall timetable, without offering some options for causing little changes on the already timetabling. For example, it would be very useful for the user to have an option to add easily time constraints in order to preserve the day(s) of selected activities. In addition, schools need to modify their timetable very often, when a teacher, or a group of students is absent. These modifications can be done "manually".
What is the situation in other countries? Do schools need to change their timetable quite often during the school year? Is the above described situation typical for many countries? Does anybody else need an easy way to add constraints for preserving the day(s) of selected activities?

Vangelis.

[Volker Dirr]

In most cases i only need to generate a timetable 2 times per year. (Just modifying from 1st to 2nd half/timetable is not possible, since the activity planning for students is too different). So I need to generate 2 different timetables per year.
Only in emergency it is needed to modify.
For example this year i needed to modify it because a teacher is sadly ill for a longer time. But modification was too difficult, so I generated again.
Luckily those ill teacher problems doesn't happen many times; and depending on if we get an emergency teacher with similar subjects or not, the timetable must be generated or modified or can also stay as it is.
If i know the "problem" already some time earlier (for example if the teacher is pregnant or if it is a projected operation in hospital) i already care about that while generating the timetable the first time. so i don't need to change it as soon as the teacher is in hospital.
If i need to modify the timetable, i do it with TiTiTo, since it is easier to do it there than with FET.
As a rough calculation i think i do some very easy modification with TiTiTo to nearly all timetables BEFORE i spread them to the teachers and students.
Large modifications are rare. In average maybe one time in five years.