Franco Raimondi

MCMAS: A Model Checker for the Verification of Multi-Agent Systems

While temporal logic in its various forms has proven essential to reason about reactive systems, agent-based scenarios are typically specified by considering high-level agents attitudes. In particular, specification languages based on epistemic logic [7], or logics for knowledge, have proven useful in a variety of areas including robotics, security protocols, web-services, etc. For example, security specifications involving anonymity [4] are known to be naturally expressible in epistemic formalisms as they explicitly state the lack of different kinds of knowledge of the principals.

Efficient online monitoring of web-service SLAs

If an organization depends on the service quality provided by another organization it often enters into a bilateral service level agreement (SLA), which mitigates outsourcing risks by associating penalty payments with poor service quality. Once these agreements are entered into, it becomes necessary to monitor their conditions, which will commonly relate to timeliness, reliability and request throughput, at run-time. We show how these conditions can be translated into timed automata. Acceptance of a timed word by a timed automaton can be decided in quadratic time and because the timed automata can operate while messages are exchanged at run-time there is effectively only a linear run-time overhead. We present an implementation to derive on-line monitors for web services automatically from SLAs using an Eclipse plugin. We evaluate the efficiency and scalability of this approach using a large-scale case study in a service-oriented computational grid.

MCMAS: a model checker for multi-agent systems

This paper presents mcmas, a model checker for Multi-Agent Systems (MAS). Differently from traditional model checkers, mcmas permits the automatic verification of specifications that use epistemic, correctness, and cooperation modalities, in addition to the standard temporal modalities. These additional modalities are used to capture properties of various scenarios (including communication and security protocols, games, etc.) that may be difficult or unnatural to express with temporal operators only; a small number of applications are presented in Section[4]. Agents are described in mcmas by means of the dedicated programming language ISPL (Interpreted Systems Programming Language). The approach is symbolic and uses ordered binary decision diagrams (obdds), thereby extending standard techniques for temporal logic to other modalities distinctive of agents. mcmas and all the examples presented in this paper are available for download [14] under the terms of the GPL license.

Automatic verification of multi-agent systems by model checking via ordered binary decision diagrams

We present a methodology for the verification of multi-agent systems, whose properties are specified by means of a modal logic that includes a temporal, an epistemic, and a modal operator to reason about correct behaviour of agents. The verification technique relies on model checking via ordered binary decision diagrams. We present an implementation and report on experimental results for two scenarios: the bit transmission problem with faults and the protocol of the dining cryptographers.

Context-Aware Adaptive Applications: Fault Patterns and Their Automated Identification

Applications running on mobile devices are intensely context-aware and adaptive. Streams of context values continuously drive these applications, making them very powerful but, at the same time, susceptible to undesired configurations. Such configurations are not easily exposed by existing validation techniques, thereby leading to new analysis and testing challenges. In this paper, we address some of these challenges by defining and applying a new model of adaptive behavior called an Adaptation Finite-State Machine (A-FSM) to enable the detection of faults caused by both erroneous adaptation logic and asynchronous updating of context information, with the latter leading to inconsistencies between the external physical context and its internal representation within an application. We identify a number of adaptation fault patterns, each describing a class of faulty behaviors. Finally, we describe three classes of algorithms to detect such faults automatically via analysis of the A-FSM. We evaluate our approach and the trade-offs between the classes of algorithms on a set of synthetically generated Context-Aware Adaptive Applications (CAAAs) and on a simple but realistic application in which a cell phones configuration profile changes automatically as a result of changes to the users location, speed, and surrounding environment. Our evaluation describes the faults our algorithms are able to detect and compares the algorithms in terms of their performance and storage requirements.

Model checking knowledge, strategies, and games in multi-agent systems

We present an OBDD-based methodology for verifying time, knowledge, and strategies in multi-agent systems specified by the formalism of interpreted systems. To this end, we investigate the interpretation of ATL and epistemic formulae in various classes of interpreted systems, we present model checking algorithms and their implementation, and report experimental results.

Symbolic Model Checking of Logics with Actions

Reasoning about agents and modalities such as knowledge and belief leads to models where different relations over states co-exist, or equivalently, where information (labels, actions) is associated to state transitions. This paper discusses how to augment classical CTL symbolic model-checking to support logics with actions such as A-CTL (action-CTL), and how this can be implemented using BDDs in tools such as the SMV/NuSMV package. Considering general action-state structures, we first propose a natural extension of CTL to actions, called Action-Restricted CTL (ARCTL) and adapt classical results from CTL to express model checking based on three functions eax, eauand eag. On these grounds, we present two different implementations of symbolic model checking with actions. The first approach encodes action-state models and logics into pure state-based models and logics, that can be checked with existing model-checkers. The second approach consists in a native implementation of the three extended operators. We report on our prototype implementation of both approaches based on NuSMV and give an overview of how this is used to model-check the temporal epistemic logic CTLK.

Service-Level Agreements for Electronic Services

The potential of communication networks and middleware to enable the composition of services across organizational boundaries remains incompletely realized. In this paper, we argue that this is in part due to outsourcing risks and describe the possible contribution of Service-Level Agreements (SLAs) to mitigating these risks. For SLAs to be effective, it should be difficult to disregard their original provisions in the event of a dispute between the parties. Properties of understandability, precision, and monitorability ensure that the original intent of an SLA can be recovered and compared to trustworthy accounts of service behavior to resolve disputes fairly and without ambiguity. We describe the design and evaluation of a domain-specific language for SLAs that tend to exhibit these properties and discuss the impact of monitorability requirements on service-provision practices.

The complexity of model checking concurrent programs against CTLK specifications

This paper presents complexity results for model checking concurrent programs against temporal-epistemic formulae. We apply these results to evaluate the complexity of verifying programs by means of two model checkers for multi-agent systems: MCMAS and Verics.

MCMAS: an open-source model checker for the verification of multi-agent systems

We present MCMAS, a model checker for the verification of multi-agent systems. MCMAS supports efficient symbolic techniques for the verification of multi-agent systems against specifications representing temporal, epistemic and strategic properties. We present the underlying semantics of the specification language supported and the algorithms implemented in MCMAS, including its fairness and counterexample generation features. We provide a detailed description of the implementation. We illustrate its use by discussing a number of examples and evaluate its performance by comparing it against other model checkers for multi-agent systems on a common case study.