Answer set programming (ASP) is a form of declarative programming that allows to succinctly formulate and efficiently solve complex problems. An intuitive extension of this formalism is communicating ASP, in which multiple ASP programs collaborate to solve the problem at hand. However, the expressiveness of communicating ASP has not been thoroughly studied. In this paper, we present a systematic study of the additional expressiveness offered by allowing ASP programs to communicate. First, we consider a simple form of communication where programs are only allowed to ask questions to each other. For the most part, we deliberately only consider simple programs, i.e. programs for which computing the answer sets is in P. We find that the problem of deciding whether a literal is in some answer set of a communicating ASP program using simple communication is NP-hard. In other words: we move up a step in the polynomial hierarchy due to the ability of these simple ASP programs to communicate and collaborate. Second, we modify the communication mechanism to also allow us to focus on a sequence of communicating programs, where each program in the sequence may successively remove some of the remaining models. This mimics a network of leaders, where the first leader has the first say and may remove models that he or she finds unsatisfactory. Using this particular communication mechanism allows us to capture the entire polynomial hierarchy. This means, in particular, that communicating ASP could be used to solve problems that are above the second level of the polynomial hierarchy, such as some forms of abductive reasoning as well as PSPACE-complete problems such as STRIPS planning.
Two other important works in the area of multi-agent ASP are @cite_24 and @cite_13 . In both @cite_24 and @cite_13 a multi-agent system is developed in which multiple agents component programs can communicate with each other. Most importantly from the point of view of our work, both approaches use ASP and have agents that are quite expressive in their own right. Indeed, in @cite_24 each agent is an Ordered Choice Logic Program (OCLP) @cite_21 and in @cite_13 each agent uses the extended answer set semantics.
@cite_24 @cite_21 @cite_13
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Multi-agent systems (MAS) can take many forms depending on the characteristics of the agents populating them. Amongst the more demanding properties with respect to the design and implementation of multi-agent system is how these agents may individually reason and communicate about their knowledge and beliefs, with a view to cooperation and collaboration. In this paper, we present a deductive reasoning multi-agent platform using an extension of answer set programming (ASP). We show that it is capable of dealing with the specification and implementation of the system's architecture, communication and the individual agent's reasoning capacities. Agents are represented as Ordered Choice Logic Programs (OCLP) as a way of modelling their knowledge and reasoning capacities, with communication between the agents regulated by uni-directional channels transporting information based on their answer sets. In the implementation of our system we combine the extensibility of the JADE framework with the flexibility of the OCT front-end to the Smodels answer set solver. The power of this approach is demonstrated by a multi-agent system reasoning about equilibria of extensive games with perfect information. The paper presents a knowledge representation formalism, in the form of a high-level Action Description Language (ADL) for multi-agent systems, where autonomous agents reason and act in a shared environment. Agents are autonomously pursuing individual goals, but are capable of interacting through a shared knowledge repository. In their interactions through shared portions of the world, the agents deal with problems of synchronization and concurrency; the action language allows the description of strategies to ensure a consistent global execution of the agents’ autonomously derived plans. A distributed planning problem is formalized by providing the declarative specications of the portion of the problem pertaining a single agent. Each of these specications is executable by a stand-alone CLP-based planner. The coordination among agents exploits a Linda infrastructure. The proposal is validated in a prototype implementation developed in SICStus Prolog. To appear in Theory and Practice of Logic Programming (TPLP). Research partially funded by GNCS-INdAM projects, MUR-PRIN: Innovative and multidisciplinary approaches for constraint and preference reasoning project; NSF grants IIS-0812267 and HRD-0420407; and grants 2009.010.0336 and 2010.011.0403. In multi-agent system, we often face incompleteness of information due to communication failure or other agent's suspension of decisions. To solve the incompleteness, we previously proposed speculative computation using abduction in the context of matter-slave multi-agent systems and gave a procedure in abductive logic programming [14]. In the work, a master agent prepares a default value for a question in advance and it performs speculative computation using the default without waiting for a reply for the question. This computation is effective unless the contradictory reply with the default is returned. However, we find that this mechanism is not sufficient for speculative computation in more general multi-agent systems such that replies can be revised according to other agents' speculative computation. In this paper, we formalize speculative computation with multi-agent belief revision and propose a correct procedure for such computation. Reasoning about capabilities, strategies and knowledge is important in the analysis of multiagent systems. Alternating-time Temporal Epistemic Logic (ATEL) was designed with this aim. Nevertheless, the original interpretation of the language suffered from some counterintuitive properties. These are due to the fact that the strategies the agent applies in worlds that he cannot distinguish may not be uniform, in the sense that the same action is applied in all indistinguishable worlds. Several refinements of the original ATEL semantics were proposed since then. In this paper we argue that the STIT framework can easily account for uniform strategies. STIT is a logic of agency that has been proposed in the 90ies in the domain of philosophy of action. It is the logic of constructions of the form "agent a sees to it that φ". To support our claim, we first present a straightforward solution in STIT logic augmented by a modal operator of knowledge. Then we offer a simplification, by introducing a modal logic of knowledge-based uniform agency, for one-step strategies, alias choices.