  Defined by Gelfond in 1991 (G91), epistemic specifications (or programs) are
an extension of logic programming under stable models semantics that
introducessubjective literals. A subjective literal al-lows checking whether
some regular literal is true in all (or in some of) the stable models of the
program, being those models collected in a setcalledworld view. One epistemic
program may yield several world views but, under the original G91 semantics,
some of them resulted from self-supported derivations. During the last eight
years, several alternative approaches have been proposed to get rid of these
self-supported worldviews. Unfortunately, their success could only be measured
by studying their behaviour on a set of common examples in the literature,
since no formal property of "self-supportedness" had been defined. To fill this
gap, we extend in this paper the idea of unfounded set from standard logic
programming to the epistemic case. We define when a world view is founded with
respect to some program and propose the foundedness property for any semantics
whose world views are always founded. Using counterexamples, we explain that
the previous approaches violate foundedness, and proceed to propose a new
semantics based on a combination of Moore's Autoepistemic Logic and Pearce's
Equilibrium Logic. The main result proves that this new semantics precisely
captures the set of founded G91 world views.
