- CaSAPI -
Credulous and Sceptical Argumentation
(Prolog Implementation)

by D. Gaertner and F. Toni



CaSAPI is a hybrid argumentation system implemented in Prolog that combines abstract and assumption-based argumentation. This work has been conducted by Dorian Gaertner and Francesca Toni, sponsored by the EU-funded ArguGRID project and by The Royal Academy on Engineering and the Leverhulme Foundation.


Download the application:

  • This argumentation system is implemented in SICStus Prolog but should be compatible with most available Prolog implementations. We make the source code available (without any guarantees, as usual, you are running it at your own risk) for private use only. For licensing information please contact the authors.

  • After starting your Prolog engine, load casapi.pl and the example file you want to run.
    For more details on how to run CaSAPI, please have a look at the ReadMe documentation.

  • We have improved CaSAPI and are currently experimenting with version v4.3. Please download CaSAPI v4.3 as a zipped archive (or as a gzipped tar archive here). It should be stable, but any feedback is highly appreciated.

  • Previous versions of CaSAPI have been presented at the ArgNMR workshop (CaSAPI v2.1) and published in the IEEE magazine (CaSAPI v3.0). These previous versions of CaSAPI have become obsolete with the distribution of CaSAPI v4.3 and are no longer maintained. Version 2.1 is a stable implementation of assumption-based argumentation but does not compute a dialectical structure. Version 3.0 does compute such a structure but is restricted to the use with patient selection functions. Version 4.3 is a fully general, hybrid argumentation system which eliminates all the restrictions of previous versions.

    • Examples:

  • The payment example from our IEEE paper demonstrating features of CaSAPI v3.

  • The motorcycle example from our COIN paper demonstrating the use of CaSAPI for agreements on goals.

  • The babyname choosing example from our COMMA paper.

  • The villa example from Prakken and Sartor's 1995 ICAIL paper "On the relation between legal language and legal argument: assumptions, applicability and dynamic priorities".

  • The prison example from Bench-Capon and Prakken's 2006 COMMA paper "Justifying actions by accruing arguments".

  • The eProcurement example from Matt et al.'s 2007 AAMAS short paper "Argumentation-based agents for eProcurement".


    • Publications directly concerning CaSAPI and its applications

  • D. Gaertner, J.A. Rodriguez and F. Toni,
    Agreeing on Institutional Goals for Multi-Agent Societies
    Fifth International workshop on Coordination, Organisation, Institution and Norms (at AAMAS 2008), Estoril, Portugal, 2008

    This paper describes how autonomous agents eager to collaborate on some business can agree on common goals of their collaboration. Two approaches, one centralised and one distributed, are presented that show how the argumentation system CaSAPI can be employed to find such an agreement on institutional goals. Subsequently, such goals can be used to define the terms of the collaboration (as norms, interactions, protocols of an institution).

  • D. Gaertner and F. Toni,
    Hybrid argumentation and its properties
    Second International Conference on Computational Models of Argument, Toulouse, France, 2008

    This paper describes a generalised, hybrid approach to argumentation that is beneficial to developing applications of argumentation where explicit justifications of claims in terms of full dialectical structures are required. In contrast to the IEEE article that described CaSAPI version 3 which only works when the selection function is patient, the computational machinery presented in this paper is general and drops that restriction. We prove its correctness via a mapping to (standard) AB-dispute derivations.

  • D. Gaertner and F. Toni,
    Computing arguments and attacks in assumption-based argumentation,
    IEEE Intelligent System, vol. 22, no. 6, Nov/Dec 2007

    This article details CaSAPI version 3, which introduces a new algorithm, providing structure to the arguments. In addition to the supporting defence set for a given initial claim, all the arguments computed in the derivation process are provided as well as their inter-relationships. The paper describes the choices made by the developers as well as the choices that the user faces. A detailed walk-through for an example using a real world scenario is provided.

  • D. Gaertner and F. Toni,
    Conflict-free normative agents using assumption-based argumentation,
    Fourth International Workshop on Argumentation in Multi-Agent Systems, Hawaii, USA, 2007

    This paper expands on the example for agent reasoning provided in the ArgNMR paper. A normative agent architecture (BDI+N) and a way to express norms are described. This agent architecture is then mapped into assumption-based argumentation in order to reason about and resolve normative conflicts. In particular, the use of various kinds of preferences is investigated.

  • D. Gaertner and F. Toni,
    CaSAPI - a system for credulous and sceptical argumentation,
    First International Workshop on Argumentation and Nonmonotonic Reasoning, Arizona, USA, 2007

    This paper describes a generalisation of assumption-based argumentation frameworks that allows for multiple contraries of a given assumption. This generalised framework is used in the CaSAPI system, which is detailed in this paper together with various application areas for the system, such as nonmonotonic reasoning, legal and practical reasoning and agent reasoning.

    • Articles describing background on (assumption-based) argumentation

  • P.M. Dung, P. Mancarella, F. Toni,
    Computing ideal sceptical argumentation
    Artificial Intelligence, Special Issue on Argumentation in Artificial Intelligence, (to appear)

  • P.M. Dung, P. Mancarella, F. Toni,
    A dialectic procedure for sceptical, assumption-based argumentation,
    First International Conference on Computational Models of Argument (COMMA 2006), September 2006

  • P.M. Dung, R.A. Kowalski, F. Toni,
    Dialectic proof procedures for assumption-based, admissible argumentation,
    Artificial Intelligence 170(2), pp 114-159, February 2006

  • Y. Dimopoulos, B. Nebel, F. Toni,
    On the Computational Complexity of Assumption-based Argumentation for Default Reasoning,
    Artificial Intelligence 141, pp 57-78, October 2002

  • A. Bondarenko, P.M. Dung, R.A. Kowalski, F. Toni,
    An abstract, argumentation-theoretic approach to default reasoning,
    Artificial Intelligence 93(1-2), pp 63-101, 1997

  • R.A. Kowalski, F. Toni,
    Abstract Argumentation,
    Artificial Intelligence and Law Journal 4(3-4), Special Issue on Logical Models of Argumentation,
    H. Prakken and G. Sartor, eds., Kluwer Academic Publishers, pp 275-296, 1996

  • A. Bondarenko, F. Toni, R.A. Kowalski,
    An Assumption-based Framework for Non-monotonic Reasoning,
    Second International Workshop on Logic Programming and Non-monotonic Reasoning,
    L.M. Pereira and A. Nerode, eds., pp 171-189, 1993


    •   Last modified: 11 July 2007