Contractions Based on Optimal Repairs (Extended Abstract)

Abstract

Removing unwanted consequences from a knowledge base has been investigated in belief change under the name contraction and is called repair in ontology engineering. Simple repair and contraction approaches based on removing statements from the knowledge base (respectively called belief base contractions and classical repairs) have the disadvantage that they are syntax-dependent and may remove more consequences than necessary. Belief set contractions do not have these problems, but may result in belief sets that have no finite representation. Similarly, optimal repairs, which are syntax-independent and maximize the retained consequences, may not exist. Our KR 2024 paper leverage advances in characterizing and computing optimal repairs of ontologies based on the description logics EL to obtain contraction operations that combine the advantages of belief set and belief base contractions. It introduces this new approach in a very general setting, and proves a characterization theorem that relates the obtained contractions with well-known rationality postulates. Then, it describes a variety of interesting instances, not only in the standard repair/contraction setting where one wants to get rid of a consequence, but also in other settings such as variants of forgetting in propositional and description logic.