Mandatory relation between ThermalZone and ThermalBoundary?

Created by: oliviertournaire

I am wondering if the boundedBy relation between ThermalZone and ThermalBoundary is really mandatory. The cardinality is set to 1..*.

However, if one just want to model a building and attached the properties isCooled or isHeated, he has to define a ThermalZone. Sounds good. However, as long as you define a ThermalZone, you are obliged to also model a ThermalBoundary. I do not think this is really necessary.

Your opinions?