Mathematically, a function is usually conceptualized as a set of tuples of objects, one for each combination of possible arguments. If there are no object constants, then we include an arbitrary object constant, say A . A Herbrand variable assignment is a variable assignment in which the universe is the Herbrand Universe for the language. The size of the Herbrand universe for a first-order language with function constants is infinite. Description Logics are a subset of relational logic.
Description Logics are decidable.