Abstract. The ability to communicate is one of the salient properties of agents. Although a number of agent communication languages (ACLs) have been developed, obtaining a suitable formal semantics for ACLs remains one of the greatest challenges of multiagent systems theory. Previous semantics have largely been mentalistic in their orientation and are based solely on the beliefs and intentions of the participating agents. Such semantics are not suitable for most multiagent applications, which involve autonomous and heterogeneous agents, whose beliefs and intentions cannot be uniformly determined. Accordingly, we present a social semantics for ACLs that gives primacy to the interactions among the agents. Our semantics is based on social commitments and is developed in temporal logic. This semantics, because of its public orientation, is essential to providing a rigorous basis for multiagent protocols. 1

Protocols represent the allowed interactions among communicating agents. Protocols are essential in applications such as electronic commerce where it is necessary to constrain the behaviors of autonomous agents. Traditional approaches, which model protocols in terms of action sequences, limit the flexibility of the agents in executing the protocols. By contrast, we develop an approach for specifying protocols in which we capture the content of the actions through agents' commitments to one another. We forrealize commitments in a variant of the event calculus. We provide operations and reasoning rules to capture the evolution of commitments through the agents' actions. Using these rules in addition to the basic event calculus axioms enables agents to reason about their actions explicitly to flexibly accommodate the exceptions and opportunities that arise at run time. This reasoning is implemented using an event calculus planner that helps us determine flexible execution paths that respect the protocol specifications.

Abstract. We develop an approach in which we model communication protocols via commitment machines. Commitment machines supply a content to protocol states and actions in terms of the social commitments of the participants. The content can be reasoned about by the agents thereby enabling flexible execution of the given protocol. We provide reasoning rules to capture the evolution of commitments through the agents ’ actions. Because of its representation of content and its operational rules, a commitment machine effectively encodes a systematically enhanced version of the original protocol, which allows the original sequences of actions as well as other legal moves to accommodate exceptions and opportunities. We show how a commitment machine can be compiled into a finite state machine for efficient execution, and prove soundness and completeness of our compilation procedure. 1

Abstract. Commitments among agents are widely recognized as an important basis for organizing interactions in multiagent systems. We develop an approach for formally representing and reasoning about commitments in the event calculus. We apply and evaluate this approach in the context of protocols, which represent the interactions allowed among communicating agents. Protocols are essential in applications such as electronic commerce where it is necessary to constrain the behaviors of autonomous agents. Traditional approaches, which model protocols merely in terms of action sequences, limit the flexibility of the agents in executing the protocols. By contrast, by formally representing commitments, we can specify the content of the protocols through the agents ’ commitments to one another. In representing commitments in the event calculus, we formalize commitment operations and domain-independent reasoning rules as axioms to capture the evolution of commitments. We also provide a means to specify protocol-specific axioms through the agents ’ actions. These axioms enable agents to reason about their actions explicitly to flexibly accommodate the exceptions and opportunities that may arise at run time. This reasoning is implemented using an event calculus planner that helps determine flexible execution paths that respect the given protocol specifications.

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Abstract. Commitments are a powerful representation for modeling multiagent interactions. Previous approaches have considered the semantics of commitments and how to check compliance with them. However, these approaches do not capture some of the subtleties that arise in real-life applications, e.g., e-commerce, where contracts and institutions have implicit temporal references. The present paper develops a rich representation for the temporal content of commitments. This enables us to capture realistic contracts and institutions rigorously, and avoid subtle ambiguities. Consequently, this approach enables us to reason about whether and when exactly a commitment is satisfied or breached and whether it is or ever becomes unenforceable. 1

In previous work [1] we presented a framework for the specification of open computational societies i.e. societies where the behaviour of the members and their interactions cannot be predicted in advance. We viewed computational systems from an external perspective, with a focus on the institutional and the social aspects of these systems. The social constraints and roles of the open societies were specified with the use of the Event Calculus. In this paper, we formalise our framework with the use of the C+ language, a formalism with explicit state transition semantics. We use the implementation of the C+ language, the Causal Calculator, a software tool for representing commonsense knowledge about action and change, to animate and validate the specifications of computational societies. We demonstrate the utility of the Causal Calculator (by specifying and executing a Contract-Net Protocol) and comment on its functionality regarding the specification of computational societies.

SoCom # 1 "on time" Abstract SoCom # 2 "cheap" Buyer Seller Abstract SoCom # 3 Buyer Seller SoCom Manager Hoosier Inc. Register me as buyer and seller Register me as buyer and seller Play Seller in AbstractSoCom #1? Yes Valvano & Co. Hot Air Bros. 8 9 Concrete SoCom created 4 6 7 "high quality" = Roles = Agents Directory Agent_id Role derived 1 Figure 2. Instantiation of a concrete SoCom 68 March 1999/Vol. 42, No. 3 COMMUNICATIONS OF THE ACM Adopt role Need to initiate Ask SoCom manager Participate No No No No No No No Ye s Yes Ye s Yes Yes Yes Ye s Register SoCom manager suggests a socom Request to create SoCom Process request Stop Stop (undefined) Stop (Failure) Instantiate and announce Receipt of a request Request to register Condition evaluation OK? Find candidates Ask candidates All say yes? Agents decision making SoCom manager's decision making Because our agents are autonomous, we must e...

Commitments provide a basis for understanding interactions in multiagent systems. Successful interoperation relies upon the interacting parties being aligned with respect to their commitments. However, alignment is nontrivial in a distributed system where agents communicate asynchronously and make different observations. We propose a formalization for commitments that ensures alignment despite asynchrony. This formalization consists of three elements: (1) a semantics of commitment operations; (2) messaging patterns that implement the commitment operations; and (3) weak constraints on agents’ behaviors to ensure the propagation of vital information. We prove that our formalization ensures alignment. We illustrate the generality of our formalization with several real-life scenarios.

Abstract. For over a decade, agent research has shown that social commitments support the definition of open multiagent systems by capturing the responsibilities that agents contract toward one another through their communications. These systems, however, rely on the assumption that agents respect the social commitments they adopt. To overcome this limitation, in this paper we investigate the role of sanctions as elements whose enforcement fosters agents ’ compliance with adopted commitments. In particular, we present a model of flexible social commitments to which sanctions are attached, and where the enforcement of sanctions act as a social control mechanism for the satisfaction of commitments. 1