Dischargeable Obligations in the 𝒮CIFF Framework

Issue title: Special issue devoted to the best paper presented at the 32nd Italian Conference on Computational Logic (CILC 2017)

Guest editors: Dario Della Monica, Aniello Murano and Luigi Sauro

Article type: Research Article

Authors: Alberti, Marco^a | Gavanelli, Marco^{b; *} | Lamma, Evelina^c | Riguzzi, Fabrizio^d | Satoh, Ken^e | Zese, Riccardo^f

Affiliations: [a] Dipartimento di Matematica e Informatica, University of Ferrara, Via Saragat 1, I-44122, Ferrara, Italy | [b] Dipartimento di Ingegneria, University of Ferrara, Via Saragat 1, I-44122, Ferrara, Italy. marco.gavanelli@unife.it | [c] Dipartimento di Ingegneria, University of Ferrara, Via Saragat 1, I-44122, Ferrara, Italy | [d] Dipartimento di Matematica e Informatica, University of Ferrara, Via Saragat 1, I-44122, Ferrara, Italy | [e] Principles of Informatics Research Division, National Institute of Informatics, Chiyoda-ku, 2-1-2, Hitotsubashi, Tokyo 101-8430, Japan | [f] Dipartimento di Ingegneria, University of Ferrara, Via Saragat 1, I-44122, Ferrara, Italy

Correspondence: [*] Address for correspondence: Dipartimento di Ingegneria, University of Ferrara, Via Saragat 1, I-44122, Ferrara, Italy

Abstract: Abductive Logic Programming (ALP) has been proven very effective for formalizing societies of agents, commitments and norms, in particular by mapping the most common deontic operators (obligation, prohibition, permission) to abductive expectations. In our previous works, we have shown that ALP is a suitable framework for representing norms. Normative reasoning and query answering were accommodated by the same abductive proof procedure, named 𝒮CIFF. In this work, we introduce a defeasible flavour in this framework, in order to possibly discharge obligations in some scenarios. Abductive expectations can also be qualified as dischargeable, in the new, extended syntax. Both declarative and operational semantics are improved accordingly, and proof of soundness is given under syntax allowedness conditions Moreover, the dischargement itself might be proved invalid, or incoherent with the rules, due to new knowledge provided later on. In such a case, a discharged expectation might be reinstated and hold again after some evidence is given. We extend the notion of dischargement to take into consideration also the reinstatement of expectations. The expressiveness and power of the extended framework, named 𝒮CIFF𝒟, is shown by modeling and reasoning upon a fragment of the Japanese Civil Code. In particular, we consider a case study concerning manifestations of intention and their rescission (Section II of the Japanese Civil Code).

Keywords: Normative reasoning, Abductive Logic Programming, Constraint Logic Programming, Dischargement of expectations

DOI: 10.3233/FI-2020-1976

Journal: Fundamenta Informaticae, vol. 176, no. 3-4, pp. 321-348, 2020