  We introduce a semantics for epistemic logic exploiting a belief base
abstraction. Differently from existing Kripke-style semantics for epistemic
logic in which the notions of possible world and epistemic alternative are
primitive, in the proposed semantics they are non-primitive but are defined
from the concept of belief base. We show that this semantics allows us to
define the universal epistemic model in a simpler and more compact way than
existing inductive constructions of it. We provide (i) a number of semantic
equivalence results for both the basic epistemic language with "individual
belief" operators and its extension by the notion of "only believing", and (ii)
a lower bound complexity result for epistemic logic model checking relative to
the universal epistemic model.
