Logic of Existentialism

The issue of representing fictional objects in knowledge representation systems is fairly relevant, since there is no universal solution for all the problems that arise. Our general goal is to make semantic interpretation of natural language as precise as possible, and interpretation of fictional terms is certainly a part of it. This paper gives a complete review for the problem of fictional and non-existent objects in logic and knowledge representation. We analyze the existent approaches to the problem, both philosophical and the actual models of the language. The author marks out the most prominent problematic cases and statements for each model, and the goal from that point is to find or create a model that will allow us to express all those sentences. First-order modal logic was considered, with the addition of actuality operator. A model for two-sorted language was given, which made it possible to express all previously collected problematic sentences without going completely out of first-order range. However, another model based on the hybrid modal language was given, which also served as a solution, and it was indirectly shown by reference that it is less expressive than other existent solutions. Due to the fact that it is not feasible to implement the resulting model into AI-based knowledge representation systems, we use OWL language for creating a set of statements and restrictions, which form out the basic framework for dealing with fictional objects.