More generally, we would like to restrict to a certain subset of elements as being sufficient for getting all other elements as least upper bounds. Hence, one defines a base of a poset "P" as being a subset "B" of "P", such that, for each "x" in "P", the set of elements in "B" that are way below "x" contains a directed set with supremum "x". The poset "P" is a continuous poset if it has some base. Especially, "P" itself is a base in this situation. In many applications, one restricts to continuous (d)cpos as a main object of study.