  We address the problem of integrating information coming from different
sources. The information consists of facts that a central server collects and
tries to combine using (a) a set of logical rules, i.e. a logic program, and
(b) a hypothesis representing the server's own estimates. In such a setting
incomplete information from a source or contradictory information from
different sources necessitate the use of many-valued logics in which programs
can be evaluated and hypotheses can be tested. To carry out such activities we
propose a formal framework based on bilattices such as Belnap's four-valued
logics. In this framework we work with the class of programs defined by Fitting
and we develop a theory for information integration.
  We also establish an intuitively appealing connection between our hypothesis
testing mechanism on the one hand, and the well-founded semantics and
Kripke-Kleene semantics of Datalog programs with negation, on the other hand.
