Tableau-based Forgetting in ALC Ontologies

In this paper, we propose two new and different approaches to forgetting variables for ALC based on the well-known tableau algorithm. The first approach computes the result of forgetting via rolling up tableaux, which also provides insights of the decidability of existence of forgetting inALC . When the result of forgetting does not exist, we provide an incremental method for computing approximations of forgetting. The second approach uses variable substitution to refine approximations of forgetting and eventually obtain the result of forgetting. This approach is capable of preserving structural information of the original ontologies and thus renders readability. As both approaches are based on the tableau algorithm, their implementations can make use of the mechanisms and optimization techniques of the existing description logic reasoners.