Semantics of knowledge-based systems with multiple forms of negation

This dissertation introduces and investigates formalisms that admit several forms of default negation which interact with each other and with explicit negation in the same application. Some theoretical aspects of this research include the investigation of the expressive power of the new formalisms and the characterization of their semantics. Practical issues include the implementation of inference mechanisms to compute in these formalisms and the calculation of the computational complexity of different reasoning tasks under the proposed semantics. One application of these formalisms is to the problem of merging several knowledge bases, each of which uses a different rule for negation, and finding answers to queries in the combined knowledge base.