Strategic Executions of Choreographed Timed Normative Multi-Agent Systems

This paper proposes a combined mechanism for coordinating agents in timed normative multi-agent systems. Timing constraints in a multi-agent system make it possible to force action execution to happen before certain time invariants are violated. In such multiagent systems we achieve coordination at two orthogonal levels with respect to states and actions. On the one hand, the behaviour of individual agents is regulated by means of social and organisational inspired concepts like norms and sanctions. On the other hand, the behaviour of sets of agents is restricted according to action-based coordination mechanisms called choreographies. In both cases, the resulting behaviour is constrained by time

Kont: Computing tradeoffs in normative multiagent systems

We propose Kont, a formal framework for comparing normative multiagent systems (nMASs) by computing tradeoffs among liveness (something good happens) and safety (nothing bad happens). Safety-focused nMASs restrict agents' actions to avoid undesired enactments. However, such restrictions hinder liveness, particularly in situations such as medical emergencies. We formalize tradeoffs using norms, and develop an approach for understanding to what extent an nMAS promotes liveness or safety. We propose patterns to guide the design of an nMAS with respect to liveness and safety, and prove their correctness. We further quantify liveness and safety using heuristic metrics for an emergency healthcare application. We show that the results of the application corroborate our theoretical development

An executable Theory of Multi-Agent Systems Refinement

Complex applications such as incident management, social simulations, manufacturing applications, electronic auctions, e-institutions, and business to business applications are pervasive and important nowadays. Agent-oriented methodology is an advance in abstractionwhich can be used by software developers to naturally model and develop systems for suchapplications. In general, with respect to design methodologies, what it may be important tostress is that control structures should be added at later stages of design, in a natural top-downmanner going from specifications to implementations, by refinement. Too much detail (be itfor the sake of efficiency) in specifications often turns out to be harmful. To paraphrase D.E.Knuth, “Premature optimization is the root of all evil” (quoted in ‘The Unix ProgrammingEnvironment’ by Kernighan and Pine, p. 91).The aim of this thesis is to adapt formal techniques to the agent-oriented methodologyinto an executable theory of refinement. The justification for doing so is to provide correctagent-based software by design. The underlying logical framework of the theory we proposeis based on rewriting logic, thus the theory is executable in the same sense as rewriting logicis. The storyline is as follows. We first motivate and explain constituting elements of agentlanguages chosen to represent both abstract and concrete levels of design. We then proposea definition of refinement between agents written in such languages. This notion of refinement ensures that concrete agents are correct with respect to the abstract ones. The advantageof the definition is that it easily leads to formulating a proof technique for refinement viathe classical notion of simulation. This makes it possible to effectively verify refinement bymodel-checking. Additionally, we propose a weakest precondition calculus as a deductivemethod based on assertions which allow to prove correctness of infinite state agents. Wegeneralise the refinement relation from single agents to multi-agent systems in order to ensure that concrete multi-agent systems refine their abstractions. We see multi-agent systemsas collections of coordinated agents, and we consider coordination artefacts as being basedeither on actions or on normative rules. We integrate these two orthogonal coordinationmechanisms within the same refinement theory extended to a timed framework. Finally, wediscuss implementation aspects.LEI Universiteit LeidenFoundations of Software Technolog

Introducing norms into practical reasoning agents

As distributed electronic systems grow to include thousands of components, from grid to peer-to-peer nodes, from (Semantic) Web services to web-apps to computation in the cloud, governance of such systems is becoming a real challenge. Modern approaches ensuring appropriate individual entities' behaviour in distributed systems, which comes from multi-agent systems (MAS) research, use norms (or regulations or policies) and/or communication protocols to express a different layer of desired or undesired states. From the individuals perspective, an agent needs to be able to function in an environment where norms act as behavioural restrictions or guidelines as to what is appropriate, not only for the individual but also for the community. In the literature the concept of norms has been defined from several perspectives: as a rule or standard of behaviour shared by members of a social group, as an authoritative rule or standard by which something is judged, approved or disapproved, as standards of right and wrong, beauty and ugliness, and truth and falsehood, or even as a model of what should exist or be followed, or an average of what currently does exist in some context. Currently there exist in the literature: 1) some treatments that formally connect the deontic aspects of norms with their operationalisation; 2) some treatments that properly distinguish between abstract norms and their (multiple) instantiations at runtime; 3) little work that formalises the operational semantics in a way that ensures flexibility in their translation to actual implementations while ensuring unambiguous interpretations of the norms; 4) little work that is suitable for both institutional-level norm monitoring and individual agent norm-aware reasoning to ensure that both are aligned; 5) few works that explore how the norms may affect the decision making process of an agent when the process includes planning mechanisms at runtime for means-ends reasoning. However, currently there is no work that includes both a formalism and an implementation covering 1-5 altogether. This thesis presents work towards the above five areas. We give a proposal to bridge the gap between a single norm formalisation and the actual mechanisms used for norm-aware planning, in order to create a normative practical reasoning mechanism. One way to do this is by reducing deontic-based norm definitions to temporal logic formulas which, in turn, can be translated into planning operational semantics. Based on these semantics, we create a mechanism to support practical normative reasoning that can be used by agents to produce and evaluate their plans. We construct a norm-oriented agent that takes into consideration operationalised norms during the plan generation phase, using them as guidelines to decide the agents future action path. To make norms influence plan generation, our norm operational semantics is expressed as an extension of the planning domain, acting as a form of temporal restrictions over the trajectories (plans) computed by the planner. We consider two approaches to do so. One implementing the semantics by using planning with constraints through paths and the other by directly translating the norms into domain knowledge to be included into the planning domain. We explore a scenario based on traffic laws in order to demonstrate the usability of our proposal. We also show how our normative frameworks are successfullyintegrated into an existing BDI agent implementation, 2APL. For each approach taken, we present quantitative experimental results and illustrate the opportunities for further research.La gestión de sistemas electrónicos distribuidos se está convirtiendo en un auténtico reto a medida que dichos sistemas crecen incluyendo múltiples componentes, desde nodos grid a peer-to-peer, servicios de la Web semántica, aplicaciones web o computación en la nube. Los enfoques modernos que aseguran un comportamiento adecuado de las entidades individuales en sistemas distribuidos, y que provienen de la investigación en sistemas multi-agentes (MAS), utilizan normas (o regulaciones o políticas) para expresar un nivel diferente de estados deseados o no deseados. Desde la perspectiva del individuo, un agente necesita poder funcionar en un entorno donde las normas actúen como restricciones o directrices de comportamiento respecto a lo que es apropiado,no únicamente para el individuo sino para la comunidad en su conjunto. En la literatura el concepto de norma se ha definido desde varias perspectivas: como una regla o estándar de comportamiento compartida por los miembros de un grupo social, como estándar de lo correcto o incorrecto, belleza o fealdad, o incluso, como un modelo que debería existir o ser seguido. En la actualidad se pueden encontrar en la literatura: 1) trabajos que conectan formalmente los aspectos deónticos de las normas con su operacionalización; 2) trabajos que distinguen adecuadamente entre normas abstractas y sus (múltiples) instanciaciones en tiempo de ejecución; 3) algún ejemplo que formaliza las semánticas operacionales de manera que se asegura la flexibilidad en su traducción a implementaciones garantizando a su vez interpretaciones no ambiguas de las normas; 4) algún trabajo que se adecúa tanto a la monitorización de normas a nivel institucional como al razonamiento basado en normas a nivel de los agentes individuales y que asegura que ambos están alineados; 5) algún trabajo que explora como las normas pueden afectar al proceso de toma de decisiones de un agente cuando el proceso incluye mecanismos de planificación en tiempo real para un razonamiento medios-fines. Sin embargo, actualmente no existe ningún enfoque que incluya formalismos e implementaciones abordando los 5 puntos al mismo tiempo. La presente tesis propone contribuciones en las cinco áreas mencionadas. Se presenta una propuesta para establecer un enlace entre la formalización de una norma y los mecanismos utilizados en la planificación basada en normas con el objetivo de crear un mecanismo de razonamiento práctico normativo. Una forma de conseguirlo es mediante la reducción de las definiciones de normas basadas en deóntica a fórmulas de lógica temporal que, a su vez, pueden ser traducidas a semánticas operacionales de planificación. Basándose en estas semánticas, se ha creado un mecanismo para dar soporte al razonamiento normativo práctico que puede ser utilizado por los agentes para producir y evaluar sus planes. Se ha construido un agente orientado a normas que tiene en consideración las normas operacionalizadas durante la fase de generación de planes, utilizándolas como directrices para decidir el futuro curso de acción del agente. Nuestras semánticas operacionales de normas se expresan como una extensión del dominio de la planificación, actuando como una forma de restricciones temporales sobre las trayectorias (planes) computadas por el planificador. Se han considerado dos enfoques para realizarlo. Uno, implementando las semánticas utilizando planificación con restricciones a través de caminos y otro, traduciendo directamente las normas en conocimiento del dominio que se incluirá en el dominio de planificación. Se explora un escenario basado en normas de circulación de tráfico para demostrar la usabilidad de nuestra propuesta. Se mostrará también como nuestro marco normativo se integra satisfactoriamente en una implementación existente de agentes BDI, 2APL. Para cada enfoque considerado, se presentan resultados experimentales cuantitativos y se ilustran las oportunidades para futuros trabajos de investigación.A mesura que els sistemes electrònics distribuïts creixen per incloure milers de components,des de nodes grid a peer-to-peer fins a serveis de la Web semàntica, aplicacions web o computació al núvol, la gestió d’aquests sistemes s’està convertint en un autèntic repte. Els enfocs moderns que asseguren el comportament apropiat de lesentitats individuals en sistemes distribuïts, que prové de la recerca en sistemes multiagents, utilitzen normes (o regulacions o polítiques) i/o protocols de comunicació perexpressar una capa diferent d’estats desitjats o no desitjats. Des de la perspectiva de l’individu, un agent necessita poder funcionar en un entorn on les normes actuïn coma restriccions de comportament o guies respecte al que és apropiat, no només per al individu sinó per a la comunitat.En la literatura el concepte de normes s’ha tractat des de diferents perspectives: com una regla o estàndard de comportament compartida pels membres d’un grup social, com una regla o estàndard autoritari pel qual alguna cosa és jutjada, aprovada o desaprovada,com estàndard del correcte i del incorrecte, bellesa i lletjor, veritat i falsedat, o inclús com un model del que hauria d’existir o ser seguit, o com una mitjana del que actualment existeix en un context donat. Actualment trobem en la literatura:1) alguns tractaments que connecten formalment els aspectes deòntics de les normes amb la seva operacionalització; 2) alguns tractaments que distingeixen adequadament entre normes abstractes i les seves (múltiples) instanciacions en temps real; 3) alguns exemples que formalitzen les semàntiques operacionals de manera que asseguren flexibilitaten la seva traducció a implementacions garantint interpretacions no ambigües de les normes; 4) alguns treballs adequats per a la monitorització de normes a nivell institucional i per al raonament basat en normes en agents individuals assegurant que ambdós estan alineats; 5) alguns treballs que exploren com les normes poden afectar el procés de presa de decisions d’un agent quan el procés inclou mecanismes de planificació en temps real per a raonament mitjans-finalitats. D’altra banda, actualment noexisteix cap enfoc que inclogui formalismes i implementacions cobrint els punts 1-5 a la vegada.Aquesta tesi presenta contribucions en les cinc àrees esmentades. Presentem una proposta per establir un enllaç entre la formalització d’una norma i els mecanismes emprats en la planificació basada en normes per tal de crear un mecanisme de raonament pràctic normatiu. Una manera d’aconseguir-ho és reduint les definicions de normes deòntiques a fórmules de lògica temporal les quals poden ser traduïdes asemàntiques de planificació operacional. Basant-nos en aquestes semàntiques, hem creat un mecanisme per donar suport al raonament normatiu pràctic que pot ser emprat per agents per produir i avaluar els seus plans. Hem construït un agent orientat a normes que pren en consideració durant la fase de generació de plans les normes operacionalitzades, utilitzant-les com a guia per decidir el futur curs d’acció de l’agent.Per tal de fer que les normes influenciïn la generació de plans, les nostres semàntiques operacionals de normes s’expressen com una extensió del domini de la planificació,actuant com una mena de restriccions temporals sobre les trajectòries (plans) computadespel planificador. Considerem dos enfocs per dur-ho a terme. Un implementant les semàntiques emprant planificació amb restriccions per mitjà de camins i l’altre traduint directament les normes en coneixement del domini a ser inclòs en el domini de planificació. Explorem un escenari basat en les normes de circulació de tràfic per demostrar la usabilitat de la nostra proposta. Mostrarem també com el nostre marc normatiu s’integra satisfactòriament en una implementació existent d’agentBDI, 2APL. Per cada enfoc considerat, presentem resultats experimentals quantitatius i il.lustrem les oportunitats per treballs de recerca futurs

On the Semantics and Verification of Normative Multi-Agent Systems

This paper presents a programming language that facilitates the implementation of coordination artifacts which in turn can be used to regulate the behaviour of individual agents. The programming language provides constructs inspired by social and organisational concepts. Depending on the scheduling mechanism of such constructs, different operational semantics can be defined. We show how one such possible operational semantics can be prototyped in Maude, which is a rewriting logic software. Prototyping by means of rewriting is important since it allows us both to design and to experiment with the language definitions. To illustrate this, we define particular properties (like enforcement and regimentation) of the coordination artifacts which we then verify with the Maude LTL model-checker

On the Semantics and Verification of Normative Multi-Agent Systems

This paper presents a programming language that facilitates the implementation of coordination artifacts which in turn can be used to regulate the behaviour of individual agents. The programming language provides constructs inspired by social and organisational concepts. Depending on the scheduling mechanism of such constructs, different operational semantics can be defined. We show how one such possible operational semantics can be prototyped in Maude, which is a rewriting logic software. Prototyping by means of rewriting is important since it allows us both to design and to experiment with the language definitions. To illustrate this, we define particular properties (like enforcement and regimentation) of the coordination artifacts which we then verify with the Maude LTL model-checker