Nicoletta Fornara

Operational specification of a commitment-based agent communication language

In this paper we propose an operational method to express the meaning of the messages exchanged among agents that interact in open environments. In an open environment, like for example the Internet, agents are usually designed by different constructors, so it is very important to define the meaning of a standard, widely accepted Agent Communication Language. We express the meaning of messages using the social notion of commitment. Commitments are defined operationally within an object-oriented paradigm. We give an operational specification of the commitment class that includes the concepts of conditional commitment and precommitment. Then we use commitment objects to define the meaning of some interesting speech acts, and give an example of their use in negotiation.

Defining interaction protocols using a commitment-based agent communication language

We propose a method for the definition of interaction protocols to be used in open multiagent systems. Starting from the assumption that language is the fundamental component of every interaction, we first propose a semantics for Agent Communication Languages based on the notion of social commitment, and then use it to define the meaning of a set of basic communicative acts. Second, we propose a verifiable and application-independent method for the definition of interaction protocols, whose main component is the specification of an interaction diagram specifying which actions may be performed by agents under given conditions. Interaction protocols fully rely on the application-independent meaning of communicative acts. We also propose a set of soundness conditions that can be used to verify whether a protocol is reasonable. Finally, our approach is exemplified by the definition of an interaction protocol for English auctions.

A simulation tool for combined rail/road transport in intermodal terminals

A simulation model of the flow of intermodal terminal units (ITUs) among and within inland intermodal terminals is presented. The intermodal terminals are interconnected by rail corridors. Each terminal serves a user catchment area via a road network. The terminal is modelled as a set of platforms, which are served by a number of gantry cranes and front lifters. The user of the simulation model defines the structure of the terminal and the train and truck arrival scenarios. The train arrivals are defined in a train timetable, while the patterns of truck arrivals for ITU delivery and pick-up can be either statistically modelled or given as a deterministic input. The simulator can be used to simulate both a single terminal and a rail network, that is, two or more interconnected terminals. During the simulation, various statistics are gathered to assess the performance of the terminal equipment, the ITU residence time, and the terminal throughput. The simulation software has been implemented as a discrete-event simulation model, using MODSIM III as development tool. The simulator tool has been developed as part of the Platform project, funded by the Directorate General VII of the European Community.

A COMMITMENT-BASED APPROACH TO AGENT COMMUNICATION

In this paper, we propose an operational method for the definition of the semantics of agent communication languages based on the notion of social commitment. Our proposal is suitable for open interaction frameworks where agents, designed by independent constructors, dynamically enter and leave different interaction systems. In this type of environment, it is crucial to define standard and commonly accepted semantics for the exchanged messages. We give an operational specification of commitment and introduce temporal propositions for the representation of the contents of commitments within an object-oriented paradigm. Then we use operations on commitments to define the meaning of a set of communicative acts that is complete with respect to Searles taxonomy of illocutionary acts, and give an example of the use of communicative acts in an interaction protocol.

Agent communication and artificial institutions

In this paper we propose an application-independent model for the definition of artificial institutions that can be used to define open multi-agent systems. Such a model of institutional reality makes us able also to define an objective and external semantics of a commitment-based Agent Communication Language (ACL). In particular we propose to regard an ACL as a set of conventions to act on a fragment of institutional reality, defined in the context of an artificial institution. Another contribution of the work presented in this paper is an operational definition of norms, a crucial component of artificial institutions. In fact in open systems interacting agents might not conform to the specifications. We regard norms as event-driven rules that when are fired by events happening in the system create or cancel a set of commitments. An interesting aspect of our proposal is that both the definition of the ACL and the definition of norms are based on the same notion of commitment. Therefore an agent capable of reasoning on commitments can reason on the semantics of communicative acts and on the system of norms.

Artificial institutions: a model of institutional reality for open multiagent systems

Software agents’ ability to interact within different open systems, designed by different groups, presupposes an agreement on an unambiguous definition of a set of concepts, used to describe the context of the interaction and the communication language the agents can use. Agents’ interactions ought to allow for reliable expectations on the possible evolution of the system; however, in open systems interacting agents may not conform to predefined specifications. A possible solution is to define interaction environments including a normative component, with suitable rules to regulate the behaviour of agents. To tackle this problem we propose an application-independent metamodel of artificial institutions that can be used to define open multiagent systems. In our view an artificial institution is made up by an ontology that models the social context of the interaction, a set of authorizations to act on the institutional context, a set of linguistic conventions for the performance of institutional actions and a system of norms that are necessary to constrain the agents’ actions.

Specifying and Enforcing Norms in Artificial Institutions

In this paper we investigate two related aspects of the formalization of open interaction systems: how to specify norms, and how to enforce them by means of sanctions. The problem of specifying the sanctions associated with the violation of norms is crucial in an open system because, given that the compliance of autonomous agents to obligations and prohibitions cannot be taken for granted, norm enforcement is necessary to constrain the possible evolutions of the system, thus obtaining a degree of predictability that makes it rational for agents to interact with the system. In our model, we introduce a construct for the definition of norms in the design of artificial institutions, expressed in terms of roles and event times, which, when certain activating events take place, is transformed into commitments of the agents playing certain roles. Norms also specify different types of sanctions associated with their violation. In the paper, we analyze the concept of sanction in detail and propose a mechanism through which sanctions can be applied.

Research directions in agent communication

Increasingly, software engineering involves open systems consisting of autonomous and heterogeneous participants or agents who carry out loosely coupled interactions. Accordingly, understanding and specifying communications among agents is a key concern. A focus on ways to formalize meaning distinguishes agent communication from traditional distributed computing: meaning provides a basis for flexible interactions and compliance checking.n Over the years, a number of approaches have emerged with some essential and some irrelevant distinctions drawn among them. As agent abstractions gain increasing traction in the software engineering of open systems, it is important to resolve the irrelevant and highlight the essential distinctions, so that future research can be focused in the most productive directions.n This article is an outcome of extensive discussions among agent communication researchers, aimed at taking stock of the field and at developing, criticizing, and refining their positions on specific approaches and future challenges. This article serves some important purposes, including identifying (1) points of broad consensus; (2) points where substantive differences remain; and (3) interesting directions of future work.

Agent communication and institutional reality

In this paper we propose to regard an Agent Communication Language (ACL) as a set of conventions to act on a fragment of institutional reality, defined in the context of an artificial institution. Within such an approach, we first reformulate a previously proposed commitment-based semantics for ACLs. In particular we show that all commonly used types of communicative acts can be defined in terms of a single basic type, namely declarations, within an artificial institution that we call Basic Institution. We then go on defining special institutions, that augment the Basic Institution by adding ontological and normative elements. Finally, as an example of a special institution we give a partial definition of the institution of English Auctions.

Representation and monitoring of commitments and norms using OWL

Monitoring the temporal evolution of obligations and prohibitions is a crucial aspect in the design of open interaction systems. In this paper we regard such obligations and prohibitions as cases of social commitment with starting points and deadlines, and propose to model them in OWL, the logical language recommended by the W3C for Semantic Web applications. In particular we propose an application-independent ontology of the notions of social commitment, temporal proposition, event, agent, role and norm, that can be used in the specification of any open interaction system. We then delineate a hybrid solution that uses the OWL ontology, SWRL rules and a Java program to dynamically monitor the temporal evolution of social commitments, taking into account the elapsing of time and the actions performed by the agents interacting within the system.