Can You Tell the Difference? Contrastive Explanations for ABox Entailments

TL;DR

This paper introduces contrastive ABox explanations for description logic ontologies, enabling understanding of why certain instances are entailed or not, by comparing relevant similarities and differences.

Contribution

It develops a novel notion of contrastive explanations for ABox reasoning, analyzing complexity and providing an initial implementation and evaluation.

Findings

Contrastive explanations focus on relevant commonalities and differences.

Complexity analysis varies with description logic variants.

Initial implementation shows practical feasibility.

Abstract

We introduce the notion of contrastive ABox explanations to answer questions of the type "Why is a an instance of C, but b is not?". While there are various approaches for explaining positive entailments (why is C(a) entailed by the knowledge base) as well as missing entailments (why is C(b) not entailed) in isolation, contrastive explanations consider both at the same time, which allows them to focus on the relevant commonalities and differences between a and b. We develop an appropriate notion of contrastive explanations for the special case of ABox reasoning with description logic ontologies, and analyze the computational complexity for different variants under different optimality criteria, considering lightweight as well as more expressive description logics. We implemented a first method for computing one variant of contrastive explanations, and evaluated it on generated problems for realistic knowledge bases.