Logic-based Technologies for Multi-agent Systems: A Systematic Literature Review

Precisely when the success of artificial intelligence (AI) sub-symbolic techniques makes them be identified with the whole AI by many non-computerscientists and non-technical media, symbolic approaches are getting more and more attention as those that could make AI amenable to human understanding. Given the recurring cycles in the AI history, we expect that a revamp of technologies often tagged as “classical AI” – in particular, logic-based ones will take place in the next few years. On the other hand, agents and multi-agent systems (MAS) have been at the core of the design of intelligent systems since their very beginning, and their long-term connection with logic-based technologies, which characterised their early days, might open new ways to engineer explainable intelligent systems. This is why understanding the current status of logic-based technologies for MAS is nowadays of paramount importance. Accordingly, this paper aims at providing a comprehensive view of those technologies by making them the subject of a systematic literature review (SLR). The resulting technologies are discussed and evaluated from two different perspectives: the MAS and the logic-based ones

Formal Specification and Automatic Verification of Multi-Agent Conditional Commitments and their Applications

Modeling agent communication using social commitments in the form of obligatory contracts among intelligent agents in a multi-agent system (MAS) provides a quintessential basis for capturing flexible and declarative interactions and helps in addressing the challenge of ensuring compliance with specifications. However, on the one hand, social commitments exclusively are not able to model agent communication actions, the cornerstone of the fundamental agent communication theory, namely speech act theory. These actions provide mechanisms for dynamic interactions and enable designers to track the evolution of active commitments. On the other hand, the designers of the system cannot guarantee the emergence of expected behaviors, such as self-contained intelligent agent complies with its protocols and honors its activated commitments. Moreover, the designers might still wish to develop effective and scalable algorithms to tackle the problem of model checking complex interactions modeled by conditional commitments and conditional commitment actions and regulated by commitment-based protocols at design time. Conditional commitments are a natural and universal frame of social commitments and cope with business conditional contracts. This dissertation is in principle about addressing two open challenging issues: 1) formally defining computationally grounded semantics for agent communication messages in terms of conditional commitments and associated actions (fulfill, cancel, release, assign and delegate), which is yet to be studied; and 2) developing a symbolic algorithm dedicated to tackle the raised model checking problem and to ensure the development of correct systems. In this dissertation, we start with distinguishing between two types of conditional commitments: weak and strong. Weak conditional commitments are those that can be activated even if the antecedents will never be satisfied, while strong conditional commitments are those that can be solely activated when there is at least one possibility to satisfy their assigned antecedents. We develop a branching-time temporal logic called CTL{cc,\alpha} that extends computation tree logic (CTL) with new modalities for representing and reasoning about the two types of conditional commitments and their actions using the formalism of interpreted systems. We present a set of valid properties, a set of reasoning rules, and a set of action postulates in order to explore the capabilities of CTL{cc,\alpha}. Furthermore, we propose a new life cycle of conditional commitments. Having a new logic (CTL{cc,\alpha}), we introduce a new symbolic algorithm to tackle the problem of its model checking. Instead of developing our algorithm from scratch, we extend the standard CTL model checking algorithm with symbolic algorithms needed for new modalities. We also investigate important theoretical results (soundness and termination) of the algorithm. Given that, we completely implement our algorithm and then assemble it on top of the symbolic model checker MCMAS, developed to automatically and directly test MAS specifications. The resulting symbolic model checker is so-called MCMAS+. We extend MCMAS's input modeling and encoding language called ISPL with shared and unshared variables needed for agent interactions and with the syntactic grammar of new modalities to produce a new one called ISPL+. We also extend the MCMAS's graphical user interface to display verified models to reduce inefficient and labor-intensive processes performed by the designers. To evaluate the performance of the developed algorithm, we analyze its time and space computational complexity. The computed time and space complexity are P-complete for explicit models and PSPACE-complete for concurrent programs. Such results are positive because model checking CTL{cc,\alpha} has the same time and space complexity of model checking CTL although CTL{cc,\alpha} extends CTL. Therefore, CTL{cc,\alpha} balances between expressive power and verification efficiency. Regarding the feasibility aspect, we apply our approach in three different application domains: business interaction protocols, health care processes, and web service compositions. The MAS paradigm is successfully employed in these domains wherein a component is represented, implemented and enacted by an agent. The proposed approach improved the employed MAS paradigm by formally modeling and automatically verifying interactions among participating agents so that the bad behaviors can be detected and then eliminated or repaired at design time and the confidence on the safety, efficiency and robustness is increased. We conduct extensive experiments to evaluate the computational performance and scalability of MCMAS+ using very large case studies. The obtained results strongly confirm the theoretical findings and make MCMAS+ practical. We finally compare our approach to other available approaches and show that it outperforms such approaches in terms of execution time, memory usage and number of considered intelligent agents

An Unexpected Journey: Towards Runtime Verification of Multiagent Systems and Beyond

The Trace Expression formalism derives from works started in 2012 and is mainly used to specify and verify interaction protocols at runtime, but other applications have been devised. More specically, this thesis describes how to extend and apply such formalism in the engineering process of distributed articial intelligence systems (such as Multiagent systems). This thesis extends the state of the art through four dierent contributions: 1. Theoretical: the thesis extends the original formalism in order to represent also parametric and probabilistic specications (parametric trace expressions and probabilistic trace expressions respectively). 2. Algorithmic: the thesis proposes algorithms for verifying trace expressions at runtime in a decentralized way. The algorithms have been designed to be as general as possible, but their implementation and experimentation address scenarios where the modelled and observed events are communicative events (interactions) inside a multiagent system. 3. Application: the thesis analyzes the relations between runtime and static verication (e.g. model checking) proposing hybrid integrations in both directions. First of all, the thesis proposes a trace expression model checking approach where it shows how to statically verify LTL property on a trace expression specication. After that, the thesis presents a novel approach for supporting static verication through the addition of monitors at runtime (post-process). 4. Implementation: the thesis presents RIVERtools, a tool supporting the writing, the syntactic analysis and the decentralization of trace expressions

Model Checking Logics of Social Commitments for Agent Communication

This thesis is about specifying and verifying communications among autonomous and possibly heterogeneous agents, which are the key principle for constructing effective open multi-agent systems (MASs). Effective systems are those that successfully achieve applicability, feasibility, error-freeness and balance between expressiveness and verification efficiency aspects. Over the last two decades, the MAS community has advocated social commitments, which successfully provide a powerful representation for modeling communications in the figure of business contracts from one agent to another. While modeling communications using commitments provides a fundamental basis for capturing flexible communications and helps address the challenge of ensuring compliance with specifications, the designers and business process modelers of the system as a whole cannot guarantee that an agent complies with its commitments as supposed to or at least not wantonly violate or cancel them. They may still wish to first formulate the notion of commitment-based protocols that regulate communications among agents and then establish formal verification (e.g., model checking) by which compliance verification in those protocols is possible. In this thesis, we address the aforementioned challenges by firstly developing a new branching-time temporal logic---called ACTL*c---that extends CTL* with modal operators for representing and reasoning about commitments and all associated actions. The proposed semantics for ACL (agent communication language) messages in terms of commitments and their actions is formal, declarative, meaningful, verifiable and semi-computationally grounded. We use ACTL*c to derive a new specification language of commitment-based protocols, which is expressive and suitable for model checking. We introduce a reduction method to formally transform the problem of model checking ACTL*c to the problem of model checking GCTL* so that the use of the CWB-NC model checker is possible. We prove the soundness of our reduction method and implement it on top of CWB-NC. To check the effectiveness of our reduction method, we report the verification results of the NetBill protocol and Contract Net protocol against some properties. In addition to the reduction method, we develop a new symbolic algorithm to perform model checking ACTL*c. To balance between expressiveness and verification efficiency, we secondly adopt a refined fragment of ACTL*c, called CTLC, an extension of CTL with modalities for commitments and their fulfillment. We extend the formalism of interpreted systems introduced to develop MASs with shared and unshared variables and considered agents' local states in the definition of a full-computationally grounded semantics for ACL messages using commitments. We present reasonable axioms of commitment and fulfillment modalities. In our verification technique, the problem of model checking CTLC is reduced into the problems of model checking ARCTL and GCTL* so that respectively extended NuSMV and CWB-NC (as a benchmark) are usable. We prove the soundness of our reduction methods and then implement them on top of the extended NuSMV and CWB-NC model checkers. To evaluate the effectiveness of our reduction methods, we verified the correctness of two business case studies. We finally proceed to develop a new symbolic model checking algorithm to directly verify commitments and their fulfillment and commitment-based protocols. We analyze the time complexity of CTLC model checking for explicit models and its space complexity for concurrent programs that provide compact representations. We prove that although CTLC extends CTL, their model checking algorithms still have the same time complexity for explicit models, and the same space complexity for concurrent programs. We fully implement the proposed algorithm on top of MCMAS, a model checker for the verification of MASs, and then check its efficiency and scalability using an industrial case study

LIPIcs, Volume 251, ITCS 2023, Complete Volume

LIPIcs, Volume 251, ITCS 2023, Complete Volum