Warda El Kholy

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.

Modeling and verifying choreographed multi-agent-based web service compositions regulated by commitment protocols

The competency to compose web services from available services is one of the most crucial problems in the paradigm of service-oriented computing. Conventional software engineering approaches and even standard languages compose web services as workflow models that control the business logic required to coordinate data over participating services. Such models would not apply to the design of multi-agent based web services, which offer high-level abstractions that support autonomy, business-level compliance, and flexible dynamic changes. In this article, we model interactions among multi-agent based web services by commitment modalities in the form of contractual obligations and devote multi-agent commitment protocols to regulate such interactions and engineer services composition. We develop and fully implement an automatic verifier by enriching the MCMAS model checker with certain symbolic algorithms to verify the correctness of protocols, given properties expressed in a temporal commitment logic, suitably extended with actions. We analyze the time and space complexity of the verifier. Finally, we present the experimental results of two case studies, adopted to check the verifiers efficiency and scalability.

Real-Time Conditional Commitment Logic

A considerably large class of multi-agent systems (MASs) employed in real-time environments requires the possibility to express time-critical properties. In this paper, we develop a system of temporal logic RTCTL\(^{cc}\), an extension of CTL modalities and interval bound until modalities with conditional commitment and their fulfillment modalities. This logic allows us to formally model the interaction among autonomous agents using conditional commitments and to combine qualitative temporal aspects together with real-time constraints (time instants or intervals) in order to permit reasoning about qualitative and quantitative requirements and their specifications. We point out that useful properties of MASs, which are required to express temporal constraints as a fundamental part of functional requirements can be expressed in RTCTL\(^{cc}\). We also argue that time-critical properties expressed in executable action languages in other contributed approaches can be expressed in RTCTL\(^{cc}\).

Formal Specification and Automatic Verification of Conditional Commitments

Developing and implementing a model checker dedicated to conditional logic with the user interface are urgent requirements for determining whether agents comply with their commitment protocols.

Verifying Multiagent-Based Web Service Compositions Regulated by Commitment Protocols

The ability to compose web services from available services is one of the most crucial problems in the service-oriented computing paradigm. Conventional software engineering approaches and even standard languages compose web services as workflow models that control the business logic required to coordinate data over participating services. Such models would not apply to the design of multiagent-based web services, which offer high-level abstractions that support autonomy, business-level compliance, and flexible dynamic changes. In this paper, we model interactions among multiagent-based services by commitment modalities in the figure of contractual obligations and devote multiagent commitment protocols to regulate such interactions and engineer services composition. We develop and fully implement a symbolic model checking algorithm by enriching the MCMAS model checker with certain symbolic algorithms to verify the correctness of protocols, given properties expressed in a temporal commitment logic, suitably extended with actions. The time complexity and space complexity of the developed algorithm are P-complete for explicit models and for PSPACE-complete concurrent programs. Finally, we report the experimental results of two case studies, adopted to check the algorithms efficiency.

SMC4AC: A New Symbolic Model Checker for Intelligent Agent Communication

Social approaches have been put forward to define semantics for intelligent agent communication messages and to tackle the shortcomings of mental approaches. Formal semantics of those social approaches can be model checked as they are focused on public behaviors instead of private mental states. Social conditional commitments are essential concepts in social approaches that can effectively model agent communications. However, conditional 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 conditional commitments. From the perspective of model checking, we need to define a formal and computationally grounded semantics for relevant social actions that can directly be applied to active conditional commitments. This manuscript describes a new symbolic model checker, SMC4AC, developed and implemented to automate the verification of interaction among intelligent agents. SMC4AC is the result of developing a new symbolic model checking algorithm devoted to CTLC, a combination of CTL and new temporal modalities to represent and reason about conditional commitments ∗Address for correspondence: Concordia Institute for Information Systems Engineering, Concordia University, Canada. †Also afiliated as Concordia Institute for Information Systems Engineering, Concordia University, Canada. Received December 2015; revised November 2016. 224 W. El Kholy et al. / SMC4AC: A New Symbolic Model Checker for Intelligent Agent Communication and common commitment actions. The core of this paper consists of a new logical language, a detailed description of the symbolic algorithms needed for commitments and their action modalities, complexity analysis, implementation and application. The implementation of our algorithm and its graphical user interface is built on top of the MCMAS symbolic model checker tailored for checking intelligent multi-agent systems. We select business processes and multi-agent interaction protocols as application domains to test and validate the effectiveness and scalability of SMC4AC. We report extensive experimental results, which confirm the theoretical findings and make SMC4AC practical.

Computational logics and verification techniques of multi-agent commitments: survey

Agent communication languages (ACLs) are fundamental mechanisms that enable agents in multi-agent systems to talk, communicate with each other in order to satisfy their individual and social goals in a cooperative and competitive manner. Social approaches are advocated to overcome the shortcomings of ACL semantics delineated by using mental approaches in the figure of agents’ mental notions. Over the last two decades, social commitments have been the subject of considerable research in some of those social approaches as they provide a powerful representation for modeling and reasoning upon multi-agent interactions in the form of mutual contractual obligations. They particularly provide a declarative, flexible, verifiable, and social semantics for ACL messages while respecting agents’ autonomy, heterogeneity, and openness.In this manuscript, we go through prominent and predominate proposals in the literature to explore the state of the art on how temporal logics can be devoted to define a formal semantics for ACL messages in terms of social commitments and associated actions. We explain each proposal and point out if and how it meets seven crucial criteria, four of them introduced by Munindar P. Singh to have a well-defined semantics for ACL messages. Far from deciding the best proposal, our aim is to present the advantages (strengths) and limitations of those proposals to designers and developers using a concrete running example and to compare between them, so that they can make the best choice with regard to their needs. We explore and evaluate current specification languages and different verification techniques that have been discussed within those proposals to, respectively, specify and verify commitment-based protocols. We also investigate logical languages of actions advocated to specify, model, and execute commitment-based protocols in other contributed proposals. Finally, we suggest some solutions that can contribute to address the identified limitations.

Model checking real-time conditional commitment logic using transformation

Abstract A new logical language for real-time conditional commitments called RTCTL cc has been developed by extending the CTL logic with interval bounded until modalities, conditional commitment modalities, and fulfillment modalities. RTCTL cc allows us to express qualitative and quantitative commitment requirements in a convenient way. These requirements can be used to model multi-agent systems (MASs) employed in environments that react properly and timely to events occurring at time instants or within time intervals. However, the timing requirements and behaviors of MASs need an appropriate way to scale and bundle and should be carefully analyzed to ensure their correctness, especially when agents are autonomous. In this paper, we develop transformation algorithms that are fully implemented in a new Java toolkit for automatically transforming the problem of model checking RTCTL cc into the problem of model checking RTCTL (real-time CTL). The toolkit engine is built on top of the NuSMV tool, effectively used to automatically verify and analyze the correctness of real-time distributed systems. We analyzed the time and space computational complexity of the RTCTL cc model checking problem. We proved the soundness and completeness of the transformation technique and experimentally evaluated the validity of the toolkit using a set of business scenarios. Moreover, we added a capability in the toolkit to automatically scale MASs and to bundle requirements in a parametric form. We experimentally evaluated the scalability aspect of our approach using the standard ordering protocol. We further validated the approach using an industrial case study.