Communicative commitments: Model checking and complexity analysis

2012

Social commitments have been extensively and effectively used to represent and model business contracts among autonomous agents having competing objectives in a variety of areas (e.g., modeling business processes and commitmentbased protocols). However, the formal verification of social commitments and their fulfillment is still an active research topic. This paper presents CTLC + that modifies CTLC, a temporal logic of commitments for agent communication that extends CTL logic to allow reasoning about communicating commitments and their fulfillment. The verification technique is based on reducing the problem of model checking CTLC + into the problem of model checking ARCTL (the combination of CTL with action formulae) and the problem of model checking GCTL * (a generalized version of CTL * with action formulae) in order to respectively use the extended NuSMV symbolic model checker and the CWB-NC automata-based model checker as a benchmark. We also prove that the reduction techniques are sound and the complexity of model checking CTLC + for concurrent programs with respect to the size of the components of these programs and the length of the formula is PSPACE-complete. This matches the complexity of model checking CTL for concurrent programs as shown by Kupferman et al. We finally provide two case studies taken from business domain along with their respective implementations and experimental results to illustrate the effectiveness and efficiency of the proposed technique. The first one is about the NetBill protocol and the second one considers the Contract Net protocol.

Simulation Modelling Practice and Theory, 2015

Though modeling and verifying Multi-Agent Systems (MASs) have long been under study, there are still challenges when many different aspects need to be considered simultaneously. In fact, various frameworks have been carried out for modeling and verifying MASs with respect to knowledge and social commitments independently. However, considering them under the same framework still needs further investigation, particularly from the verification perspective. In this article, we present a new technique for model checking the logic of knowledge and commitments (CTLKC + ). The proposed technique is fully-automatic and reduction-based in which we transform the problem of model checking CTLKC + into the problem of model checking an existing logic of action called ARCTL. Concretely, we construct a set of transformation rules to formally reduce the CTLKC + model into an ARCTL model and CTLKC + formulae into ARCTL formulae to get benefit from the extended version of NuSMV symbolic model checker of ARCTL. Compared to a recent approach that reduces the problem of model checking CTLKC + to another logic of action called GCTL ⁄ , our technique has better scalability and efficiency. We also analyze the complexity of the proposed model checking technique. The results of this analysis reveal that the complexity of our reduction-based procedure is PSPACE-complete for local concurrent programs with respect to the size of these programs and the length of the formula being checked. From the time perspective, we prove that the complexity of the proposed approach is P-complete with regard to the size of the model and length of the formula, which makes it efficient. Finally, we implement our model checking approach on top of extended NuSMV and report verification results for the verification of the NetBill protocol, taken from business domain, against some desirable properties. The obtained results show the effectiveness of our model checking approach when the system scales up.

Social commitments have been widely studied to represent business contracts among agents with different competing objectives in communicating multi-agent systems. However, their formal verification is still an open issue. This paper proposes a novel model-checking algorithm to address this problem. We define a new temporal logic, CTLC, which extends CTL with modalities for social commitments and their fulfillment and violation. The verification technique is based on symbolic model checking that uses ordered binary decision diagrams to give a compact representation of the system. We also prove that the problem of model checking CTLC is polynomial-time reducible to the problem of model checking CTLK, the combination of CTL with modalities for knowledge. We finally present the full implementation of the proposed algorithm by extending the MCMAS symbolic model checker and report on the experimental results obtained when verifying the NetBill protocol.

Applied Intelligence, 2014

Both knowledge and social commitments have received considerable attention in Multi-Agent Systems (MASs), specially for multi-agent communication. Plenty of work has been carried out to define their semantics. However, the relationship between social commitments and knowledge has not been investigated yet. In this paper, we aim to explore such a relationship from the semantics and model checking perspectives with respect to CTLK logic (an extension of CTL logic with modality for reasoning about knowledge) and CTLC logic (an extension of CTL with modalities for reasoning about commitments and their fulfillments). To analyze this logical relationship, we simply combine the two logics in one new logic named CTLKC. The purpose of such a combination is not to advocate a new logic, but only to express and figure out some reasoning postulates merging both knowledge and commitments as they are currently defined in the literature. By so doing, we identify some paradoxes in the new logic showing that simply combining current versions of commitment and knowledge logics results in a logical language that violates some fundamental intuitions. Consequently, we propose CTLKC + , a new logic that fixes the identified paradoxes and allows us to reason about social commitments and knowledge simultaneously in a consistent manner. Furthermore, we address the problem of model checking CTLKC + by reducing it to the problem of model checking GCTL * , a generalized version of CTL * with action formulae. By doing so, we directly benefit from CWB-NC, the model checker of GCTL * . Using this reduction, we also prove that the computational complexity of model checking CTLKC + is still PSPACE-complete for concurrent programs as the complexity of model checking CTLK and CTLC separately.

Expert Systems with Applications, 2013

Although several approaches have been proposed to specify multi-agent commitmentbased protocols that capture flexible and rich interactions among autonomous and heterogeneous agents, very few of them synthesize their formal specification and automatic verification in an integrated framework. In this paper, we present a new logic-based language to specify commitment-based protocols, which is derived from ACTL * c , a logic extending CTL * with modalities to represent and reason about social commitments and their actions. We present a reduction technique that formally transforms the problem of model checking ACTL * c to the problem of model checking GCTL * (an extension of CTL * with action formulae). We prove that the reduction technique is sound and we fully implement it on top of the CWB-NC model checker to automatically verify the NetBill protocol, a motivated and specified example in the proposed specification language. We also apply the proposed technique to check the compliance of another protocol: the Contract Net protocol with given properties and report and discuss the obtained results. We finally develop a new symbolic algorithm to perform model checking dedicated to the proposed logic.

Logics in Artificial Intelligence, 2004

In this paper we address the problem of specifying and verifying systems of communicating agents in a Dynamic Linear Time Temporal Logic (DLTL). This logic provides a simple formalization of the communicative actions in terms of their effects and preconditions. Furthermore it allows to specify interaction protocols by means of temporal constraints representing permissions and commitments. Agent programs, when known, can be formulated in DLTL as complex actions (regular programs). The paper addresses several kinds of verification problems including the problem of compliance of agents to the protocol, and describes how they can be solved by model checking in DLTL using automata.

Lecture Notes in Computer Science, 2003

In this paper we develop a logical framework for specifying and verifying systems of communicating agents. The framework is based on a Dynamic Linear Time Temporal Logic (DLTL). It provides a simple formalization of the communicative actions in terms of their effects and preconditions and the specification of an interaction protocol by means of temporal constraints. We adopt a social approach to agent communication (as proposed by Singh): communication can be described in terms of changes in the social relations between participants, and protocols in terms of creation, manipulation and satisfaction of commitments among agents. The description of the interaction protocol and of communicative actions is given in a temporal action theory, and agent programs, when known, can be specified as complex actions (regular programs in DLTL). The paper addresses several kinds of verification problems (including the problem of compliance of agents to the protocol), which can be formalized either as validity or as satisfiability problems in the temporal logic and can be solved by model checking techniques. 1 A closely related approach was proposed by Labrou and Finin [15] to define a semantics for KQML.

Scientific Issues, 2016

We propose an SMT-based bounded model checking (BMC) technique for the existential fragments of CCTL ⋆ K-an epistemic temporal logic extended to include modalities for different social commitments-and for multi-agent systems modelled by Communication Interpreted Systems (CIS). Furthermore, we exemplify the use of the technique by means of the NetBill protocol, a popular example in the MAS literature related to the modelling of business processes.

Computation

Innumerable industries now use multi-agent systems (MASs) in various contexts, including healthcare, security, and commercial deployments. It is challenging to select reliable business protocols for critically important safety-related systems (e.g., in healthcare). The verification and validation of business applications is increasingly explored concerning multi-agent systems’ group social commitments. This study explains a novel extended reduction verification method to model-check business applications’ critical specification rules using action restricted computation tree logic (ARCTL). In particular, we aim to conduct the verification process for the CTLGC logic using a reduction algorithm and show its effectiveness to handle MASs with huge models, thus, showing its importance and applicability in large real-world applications. To do so, we need to transform the CTLGC model to an ARCTL model and the CTLGC formulas into ARCTL formulas. Thus, the developed method was verified with ...

Applied Soft Computing

Interaction among autonomous agents in Multi-Agent Systems (MASs) is a key aspect for agents to coordinate with one another. Social approaches, as opposed to the mental approaches, have recently received a considerable attention in the area of agent communication. They exploit observable social commitments to develop a verifiable formal semantics through which communication protocols can be specified. Developing and implementing algorithmic model checking for social commitments have been recently addressed. However, model checking social commitments in the presence of uncertainty is yet to be investigated. In this paper, we propose a model checking technique for verifying social commitments in uncertain settings. Social commitments are specified in a modal logical language called Probabilistic Computation Tree Logic of Commitments (PCTLC). The modal logic PCTLC extends PCTL, the probabilistic extension of CTL, with modalities for commitments and their fulfillments. The proposed veri...