Thirty years of Epistemic Specifications

TL;DR

This paper reviews thirty years of development in epistemic specifications, discussing their semantics, applications, and future challenges in knowledge representation and reasoning.

Contribution

It provides a comprehensive overview of the evolution, semantics, and properties of epistemic specifications, clarifying the current state of the art and future research directions.

Findings

Multiple semantics proposals with varying properties

Analysis of the strengths and limitations of existing semantics

Identification of open challenges for future research

Abstract

The language of epistemic specifications and epistemic logic programs extends disjunctive logic programs under the stable model semantics with modal constructs called subjective literals. Using subjective literals, it is possible to check whether a regular literal is true in every or some stable models of the program, those models, in this context also called \emph{belief sets}, being collected in a set called world view. This allows for representing, within the language, whether some proposition should be understood accordingly to the open or the closed world assumption. Several attempts for capturing the intuitions underlying the language by means of a formal semantics were given, resulting in a multitude of proposals that makes it difficult to understand the current state of the art. In this paper, we provide an overview of the inception of the field and the knowledge representation and reasoning tasks it is suitable for. We also provide a detailed analysis of properties of proposed semantics, and an outlook of challenges to be tackled by future research in the area. Under consideration in Theory and Practice of Logic Programming (TPLP)