In the combination approach, we take the union of the knowledge bases (a finite set of logical formulas).
Baral, Kraus, Minker and Subrahmanian[5][2] present algorithms for combining knowledge-bases consisting of first-order theories, and to resolve inconsistencies among them.Subrahamanian[3] presents a uniform theoretical framework, based on annotated logics, for combining multiple knowledge bases which may have inconsistencies, uncertainties, and nonmonotonic modes of negation.
Meyer, Ghose and Chopra[15] relate belief-merging to social choice, elections and preference aggregation.
Everaere, Konieczny and Marquis[17] study belief-merging operators in settings in which the different information sources are strategic, and may try to change their stated beliefs in order to influence the outcome.
Haret, Lackner, Pfandler and Wallner[20] study belief-merging operators that satisfy fairness properties, similar to justified representation.