Set off by comma

Ø Black cat likes tuna.
This is our way and is applicable to both a case of general meaning and a case of defining.
The cat, which is black, likes tuna.
In other words, this sentence combines two different concepts. I would make two clauses separately. The universe of discourse made up of only one thing? I'd say no.

I could say that we don't have the room or the universe of discourse you mentioned above. Or we may stand between the room and the universe of discourse whenever we hear any statement that is unclear to judge. Or, with the clause SamData has only one graphics program, I might have dropped into a black hole that provides us with generalization. I took the clause somewhat a general/broad meaning that describes how SamData is. Therefore I said: I thought SamData has only one program to sell as their commercial product and Black cats like tuna?

However,

the whole room full of cats
they're referring to the one cat that's there in the room,

now it's clear that there are two types of room. And, in the room of non-defining,

they're referring to the one cat that's there in the room,
therefore,
he or she can figure out which cat likes tuna.