Skills definition

[braktar]

The current model expects the jobs, shipments to have all or none the field skills
Moreover, having a field with an empty array returns an error Missing skills.
It is expected to provide at least a dummy 'skill' for every jobs and vehicles.

My expectation was, that a vehicle with an empty array of skills could serve jobs or shipments without particular need (with an empty array of skills as well). And a job with an empty set of skills can be served by any vehicle.

[jcoupey]

Yes, there is an input check that enforces that skills are either always or never provided. And currently an empty skills array behaves as if there were no skills key at all.

I remember I had to make this choice back when skills were introduced a while ago. The rationale for enforcing always having values was that a default behavior seemed inconsistent with other constraints. If no skills (or empty skills array) for a vehicle means that this vehicle can only serve tasks with empty skills, then it's actually imposing a strong constraint. Whereas for other constraints (think TW), not defining the key defaults to no constraint. I was worried that the "no key -> no constraint" approach for skills could confuse users into thinking that a vehicle without specific skills can actually serve any task.

a vehicle with an empty array of skills could serve jobs or shipments without particular need (with an empty array of skills as well)

On the other hand, this is a clear way to describe a sound behavior, and it's actually consistent with the current skills documentation stating that "job j is eligible to vehicle v iff j.skills is included in v.skills" (an empty array is included in any array).

Also this change would be backward compatible (only opening new easier ways to model certain situations). The icing on the cake is that it would only be a matter of loosening the above checks because the current vehicle/task compatibility checks would work out of the box with empty arrays (except of course for the assert):

vroom/src/structures/vroom/input/input.cpp

Lines 322 to 330 in 313e1f9

	bool is_compatible = true;
	assert(!jobs[j].skills.empty());
	for (const auto& s : jobs[j].skills) {
	if (v_skills.find(s) == v_skills.end()) {
	is_compatible = false;
	break;
	}
	}
	_vehicle_to_job_compatibility[v][j] = is_compatible;