Mohamed El-Menshawy

Verifying conformance of multi-agent commitment-based protocols

Although several approaches have been proposed to specify multi-agent commitment-based 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.

Verifiable semantic model for agent interactions using social commitments

Existing approaches about defining formal semantics of commitment usually consider operations as axioms or constrains on top of the commitment semantics, which fail to capture the meaning of interactions that are central to real-life business scenarios. Furthermore, existing semantic frameworks using different logics do not gather the full semantics of commitment operations and semantics of social commitments within the same framework. This paper develops a novel unified semantic model for social commitments and their operations. It proposes a logical model based on a new logic extending CTL* with commitments and operations to specify agent interactions. We also propose a new definition of assignment and delegation operations by considering the relationship between the original and new commitment contents. We prove that the proposed model satisfies some properties that are desirable when modeling agent interactions in MASs and introduce a NetBill protocol as a running example to clarify the automatic verification of this model. Finally, we present an implementation and report on experimental results of this protocol using the NuSMV and MCMAS symbolic model checkers.

Communicative commitments: Model checking and complexity analysis

We refine CTLC, a temporal logic of social commitments that extends CTL to allow reasoning about commitments agents create when communicating and their fulfillment. We present axioms of commitments and their fulfillment and provide the associated BDD-based model checking algorithms. We also analyze the time complexity of CTLC model checking in explicit models (i.e., Kripke-like structures) and its space complexity for concurrent programs, which provide compact representations. We prove that although CTLC extends CTL, their model checking algorithms still have the same time complexity for explicit models, which is P-complete with regard to the size of the model and length of the formula, and the same complexity for concurrent programs, which is PSPACE-complete with regard to the size of the components of these programs. We fully implemented the proposed algorithms on top of MCMAS, a model checker for the verification of multi-agent systems, and provide in this paper simulation results of an industrial case study.

Symbolic model checking commitment protocols using reduction

Using model checking to verify that interaction protocols have given properties is widely recognized as an important issue in multiagent systems where autonomous and heterogeneous agents need to successfully regulate and coordinate their interactions. In this paper, we investigate the use of symbolic model checkers to verify the compliance of a special kind of interaction protocols called commitment protocols with some properties such as liveness and safety. These properties are expressed as formulae in a new temporal logic, called CTLC, which extends the temporal logic CTL with modality for social commitments. Our approach shows that the problem of model checking CTLC can be reduced to the problem of model checking either CTLK or ARCTL, which are extensions of CTL. We finally present an implementation and report on the experimental results of verifying the Contract Net Protocol modeled in terms of commitments and associated actions using the symbolic model checkers MCMAS and extended NuSMV.

Model checking probabilistic social commitments for intelligent agent communication

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 verification method is a reduction-based model checking technique to the model checking of PCTL. The technique is based upon a set of reduction rules that translate PCTLC formulae to PCTL formulae to take benefit of existing model checkers such as PRISM. Proofs that confirm the soundness of the reduction technique are presented. We also present rules that transform our new version of interpreted systems into models of Markov Decision Processes (MDPs) to be suitable for the PRISM tool. We implemented our approach on top of the PRISM model checker and verified some given properties for the Oblivious Transfer Protocol from the cryptography domain. Our simulation demonstrates the effectiveness of our approach in verifying and model checking social commitments in the presence of uncertainty. We believe that the proposed formal verification technique will advance the literature of social commitments in such a way that not only representing social commitments in uncertain settings is doable, but also verifying them in such settings becomes achievable.

A New Semantics of Social Commitments Using Branching Space-Time Logic

Commitments based on branching time logic are powerful representations for modeling multi-agent interactions. Current approaches into commitments have conceived these representations and evolved the commitments as “world-wide” states called moments. These approaches do not capture the space and space-like dimensions and ignore the causal relation between the participating agents. This paper presents a significant step towards developing a new logical semantics of social commitments based on Branching Space-Time (BST) logic. The contributions of this paper are threefold: first, we reformulate BST-logic from philosophical perspective to computational logic being used in computer science discipline; second, we enhance this logic with social commitments (propositional and conditional) and space-like modalities; and third, we present a new semantics model for social commitments and two-party operations that manipulate commitments in the same framework.

Model checking commitment protocols

We investigate the problem of verifying commitment protocols that are widely used to regulate interactions among cognitive agents by means of model checking. We present a new logic-based language to specify commitment protocols, which is derived from extending CTL* with modalities for social commitments and associated actions. We report on the implementation of the NetBill protocol--a motivated and specified example in the proposed language--using three model checkers (MCMAS, NuSMV, and CWB-NC) and compare the experimental results obtained.