This paper studies, in a comprehensive manner, different aspects of extended disjunctive logic programs, that is, programs whose clauses are of the form l ₁ ... l _k l _k+1, ..., l _m , not l _m+1,..., not l _n , where l ₁,..., l _n are literals (i.e. atoms and classically negated atoms), and not is the negation-by-default operator. The explicit use of classical negation suggests the introduction of a new truth value, namely, logical falsehood (in contrast to falsehood-by-default) in the semantics. General techniques are described for extending the model, fixpoint, and proof theories of an arbitrary semantics of normal disjunctive logic programs to cover the class of extended programs. Illustrations of these techniques are given for stable models, disjunctive well-founded and stationary semantics. Also, the declarative complexity of the extended programs as well as the algorithmic complexity of the proof procedures are discussed.