Marek and Truszczyński have introduced an interesting mechanism for specifying revisions of knowledge bases by means of logic programs. Here we extend their idea to allow for confidence factors, multiple experts, and so on. The appropriate programming mechanism turns out to be annotated logic programs and the appropriate semantic tool, bilattices. This may be the first example of a setting in which both notions arise naturally, and complement each other. We also show that several of the results of Marek and Truszczyński turn out to be essentially algebraic, once the proper setting has been formulated.