These kinds of constraints fall into the shaded region between the
<#331#>hard<#331#> and <#332#>soft<#332#> constraints in the sense that they do not
directly deal with time conflicts as do the hard type, but nonetheless
have a high penalty attached to them (though not as
high as that associated with the hard constraints). In the final
schedule the penalty of these constraints should be minimized and
preferably reduced to zero.
In short, these kind of constraints should be satisfied but are
nevertheless relaxable. Some examples of medium constraints:
- For each student, balance the three-day (<#334#>Mon, Wed, Fri<#334#>)
as well as the two-day (<#335#>Tue, Thu<#335#>) schedules.
- Balance or spread out the lectures over the week.
- Classes may request contiguous time slots.
- Classes may be grouped with other classes.
- It is not the case, in general, that all classrooms are
available for all subjects. In reality, many subjects require a
special purpose rooms.
Constraints involving classes that are not available during certain
time period(s) due to the unavailability of their instructors at those
times are harder than constraints of no overlapping classes involving
common student(s). Also constraints involving students preferences
fall in this category.