Towards formal models and languages for verifiable Multi-Robot Systems

Incorrect operations of a Multi-Robot System (MRS) may not only lead to unsatisfactory results, but can also cause economic losses and threats to safety. These threats may not always be apparent, since they may arise as unforeseen consequences of the interactions between elements of the system. This call for tools and techniques that can help in providing guarantees about MRSs behaviour. We think that, whenever possible, these guarantees should be backed up by formal proofs to complement traditional approaches based on testing and simulation. We believe that tailored linguistic support to specify MRSs is a major step towards this goal. In particular, reducing the gap between typical features of an MRS and the level of abstraction of the linguistic primitives would simplify both the specification of these systems and the verification of their properties. In this work, we review different agent-oriented languages and their features; we then consider a selection of case studies of interest and implement them useing the surveyed languages. We also evaluate and compare effectiveness of the proposed solution, considering, in particular, easiness of expressing non-trivial behaviour.Comment: Changed formattin

Abstraction in Model Checking Multi-Agent Systems

This thesis presents existential abstraction techniques for multi-agent systems preserving temporal-epistemic specifications. Multi-agent systems, defined in the interpreted system frameworks, are abstracted by collapsing the local states and actions of each agent. The goal of abstraction is to reduce the state space of the system under investigation in order to cope with the state explosion problem that impedes the verification of very large state space systems. Theoretical results show that the resulting abstract system simulates the concrete one. Preservation and correctness theorems are proved in this thesis. These theorems assure that if a temporal-epistemic formula holds on the abstract system, then the formula also holds on the concrete one. These results permit to verify temporal-epistemic formulas in abstract systems instead of the concrete ones, therefore saving time and space in the verification process. In order to test the applicability, usefulness, suitability, power and effectiveness of the abstraction method presented, two different implementations are presented: a tool for data-abstraction and one for variable-abstraction. The first technique achieves a state space reduction by collapsing the values of the domains of the system variables. The second technique performs a reduction on the size of the model by collapsing groups of two or more variables. Therefore, the abstract system has a reduced number of variables. Each new variable in the abstract system takes values belonging to a new domain built automatically by the tool. Both implementations perform abstraction in a fully automatic way. They operate on multi agents models specified in a formal language, called ISPL (Interpreted System Programming Language). This is the input language for MCMAS, a model checker for multi-agent systems. The output is an ISPL file as well (with a reduced state space). This thesis also presents several suitable temporal-epistemic examples to evaluate both techniques. The experiments show good results and point to the attractiveness of the temporal-epistemic abstraction techniques developed in this thesis. In particular, the contributions of the thesis are the following ones: • We produced correctness and preservation theoretical results for existential abstraction. • We introduced two algorithms to perform data-abstraction and variable-abstraction on multi-agent systems. • We developed two software toolkits for automatic abstraction on multi-agent scenarios: one tool performing data-abstraction and the second performing variable-abstraction. • We evaluated the methodologies introduced in this thesis by running experiments on several multi-agent system examples

Model checking multi-agent systems

A multi-agent system (MAS) is usually understood as a system composed of interacting autonomous agents. In this sense, MAS have been employed successfully as a modelling paradigm in a number of scenarios, especially in Computer Science. However, the process of modelling complex and heterogeneous systems is intrinsically prone to errors: for this reason, computer scientists are typically concerned with the issue of verifying that a system actually behaves as it is supposed to, especially when a system is complex. Techniques have been developed to perform this task: testing is the most common technique, but in many circumstances a formal proof of correctness is needed. Techniques for formal verification include theorem proving and model checking. Model checking techniques, in particular, have been successfully employed in the formal verification of distributed systems, including hardware components, communication protocols, security protocols. In contrast to traditional distributed systems, formal verification techniques for MAS are still in their infancy, due to the more complex nature of agents, their autonomy, and the richer language used in the specification of properties. This thesis aims at making a contribution in the formal verification of properties of MAS via model checking. In particular, the following points are addressed: • Theoretical results about model checking methodologies for MAS, obtained by extending traditional methodologies based on Ordered Binary Decision Diagrams (OBDDS) for temporal logics to multi-modal logics for time, knowledge, correct behaviour, and strategies of agents. Complexity results for model checking these logics (and their symbolic representations). • Development of a software tool (MCMAS) that permits the specification and verification of MAS described in the formalism of interpreted systems. • Examples of application of MCMAS to various MAS scenarios (communication, anonymity, games, hardware diagnosability), including experimental results, and comparison with other tools available

FLACOS’08 Workshop proceedings

The 2nd Workshop on Formal Languages and Analysis of Contract-Oriented Software (FLACOS’08) is held in Malta. The aim of the workshop is to bring together researchers and practitioners working on language-based solutions to contract-oriented software development. The workshop is partially funded by the Nordunet3 project “COSoDIS” (Contract-Oriented Software Development for Internet Services) and it attracted 25 participants. The program consists of 4 regular papers and 10 invited participant presentations

ISS Space Plasma Laboratory: An ISS instrument package for investigating the opening/closing of solar and heliospheric magnetic fields

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140428/1/6.2014-1422.pd

Verification of logical consistency in robotic reasoning

Most autonomous robotic agents use logic inference to keep themselves to safe and permitted behaviour. Given a set of rules, it is important that the robot is able to establish the consistency between its rules, its perception-based beliefs, its planned actions and their consequences. This paper investigates how a robotic agent can use model checking to examine the consistency of its rules, beliefs and actions. A rule set is modelled by a Boolean evolution system with synchronous semantics, which can be translated into a labelled transition system (LTS). It is proven that stability and consistency can be formulated as computation tree logic (CTL) and linear temporal logic (LTL) properties. Two new algorithms are presented to perform realtime consistency and stability checks respectively. Their implementation provides us a computational tool, which can form the basis of efficient consistency checks on-board robots

Specifying and Verifying Contract-driven Composite Web Services: a Model Checking Approach

As a promising computing paradigm in the new era of cross-enterprise e-applications, web services technology works as plugin mode to provide a value-added to applications using Service-Oriented Computing (SOC) and Service-Oriented Architecture (SOA). Verification is an important issue in this paradigm, which focuses on abstract business contracts and where services’ behaviors are generally classified in terms of compliance with / violation of their contracts. However, proposed approaches fail to describe in details both compliance and violation behaviors, how the system can distinguish between them, and how the system reacts after each violation. In this context, specifying and automatically generating verification properties are challenging key issues. This thesis proposes a novel approach towards verifying the compliance with contracts regulating the composition of web services. In this approach, properties against which the system is verified are generated automatically from the composition’s implementation. First, Business Process Execution Language (BPEL)that specifies actions within business processes with web services is extended to create custom activities, called labels. Those labels are used as means to represent the specifications and mark the points the developer aims to verify. A significant advantage of this labeling is the ability to target specific points in the design to be verified, which makes this verification very focused. Second, new translation rules from the extended BPEL into ISPL, the input language of the MCMAS model checker, are provided so that model checking the behavior of our contract-driven compositions is possible. The verification properties are expressed in the CTLC logic, which provides a powerful representation for modeling composition contracts using commitment-based multiagent interactions. A detailed case study with experimental results are also reported ins the thesis

Using multi-agent systems to go beyond temporal patterns verification

A key step in formal verification is the translation of requirements into logic formulae. Various flavours of temporal logic are commonly used in academia and in industry to capture, among others, liveness and safety requirements. In the past two decades there has been a substantial amount of work in the area of verification of extensions of temporal logic. In this column I will provide a high level overview of some work in this area, focussing in particular on the verification of temporal-epistemic properties, showing how temporal-epistemic logics can be used to capture requirements that are common in many concrete systems, and describing a model checker for multi-agent systems called MCMAS