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1. Mandrake: multiagent systems as a basis for programming fault-tolerant decentralized applications

   https://doi.org/10.1007/s10458-021-09540-8  

   Christie, V, Samuel H.; Chopra, Amit K.; Singh, Munindar P. (February 2022, Autonomous Agents and Multi-Agent Systems)

   Abstract We conceptualize adecentralizedsoftware application as one constituted fromautonomousagents that communicate viaasynchronousmessaging. Modern software paradigms such as microservices and settings such as the Internet of Things evidence a growing interest in decentralized applications. Constructing a decentralized application involves designing agents as independent local computations that coordinate successfully to realize the application’s requirements. Moreover, a decentralized application is susceptible to faults manifested as message loss, delay, and reordering. We contributeMandrake, a programming model for decentralized applications that tackles these challenges without relying on infrastructure guarantees. Specifically, we adopt the construct of aninformation protocolthat specifies messaging between agents purely in causal terms and can be correctly enacted by agents in a shared-nothing environment over nothing more than unreliable, unordered transport. Mandrake facilitates (1) implementing protocol-compliant agents by introducing a programming model; (2) transforming protocols into fault-tolerant ones with simple annotations; and (3) a declarative policy language that makes it easy to implement fault-tolerance in agents based on the capabilities in protocols. Mandrake’s significance lies in demonstrating a straightforward approach for constructing decentralized applications without relying on coordination mechanisms in the infrastructure, thus achieving some of the goals of the founders of networked computing from the 1970s. 

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2. Deserv: Decentralized Serverless Computing

   Christie, Samuel H.; Chopra, Amit K.; Singh, Munindar P. (January 2021, Proceedings of the 19th IEEE International Conference on Web Services)

   null (Ed.)

   A decentralized application involves multiple autonomous principals, e.g., humans and organizations. Autonomy motivates (1) specifying a decentralized application via a protocol that captures the interactions between the principals, and (2) a programming model that enables each principal to independently (from other principals) construct its own protocol-compliant agent. An agent encodes its principal's decision making and represents it in the application. We contribute Deserv, the first protocol-based programming model for decentralized applications that is suited to the cloud. Specifically, Deserv demonstrates how to leverage function-as-a-service (FaaS), a popular serverless programming model, to implement agents. A notable feature of Deserv is the use declarative protocols to specify interactions. Declarative protocols support implementing stateful agents in a manner that naturally exploits the concurrency and autoscaling benefits offered by serverless computing. 

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3. Kiko: Programming Agents to Enact Interaction Protocols

   Christie, Samuel H.; Singh, Munindar P.; Chopra, Amit K. (May 2023, Proceedings of the International Conference on Autonomous Agents and MultiAgent Systems (AAMAS)

   Realizing a multiagent system involves implementing member agents who interact based on a protocol while making decisions in a decentralized manner. Current programming models for agents offer poor abstractions for decision making and fail to adequately bridge an agent’s internal decision logic with its public decisions. We present Kiko, a protocol-based programming model for agents. To implement an agent, a programmer writes one or more decision makers, each of which chooses from among a set of valid decisions and makes mutually compatible decisions on what messages to send. By completely abstracting away the underlying communication service and by supporting practical decision-making patterns, Kiko enables agent developers to focus on business logic. We provide an operational semantics for Kiko and establish that Kiko agents are protocol compliant and able to realize any protocol enactment. 

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4. Invited Paper: Failure is (literally) an Option: Atomic Commitment vs Optionality in Decentralized Finance

   https://doi.org/2110.09872  

   engel, daniel; xue, yingjie (November 2021, SSS 2021: 23rd International Symposium on Stabilization, Safety, and Security of Distributed Systems)

   null (Ed.)

   Many aspects of blockchain-based decentralized finance can be understood as an extension of classical distributed computing. In this paper, we trace the evolution of two interrelated notions: failure and fault-tolerance. In classical distributed computing, a failure to complete a multi-party protocol is typically attributed to hardware malfunctions. A fault-tolerant protocol is one that responds to such failures by rolling the system back to an earlier consistent state. In the presence of Byzantine failures, a failure may be the result of an attack, and a fault-tolerant protocol is one that ensures that attackers will be punished and victims compensated. In modern decentralized finance however, failure to complete a protocol can be considered a legitimate option, not a transgression. A fault-tolerant protocol is one that ensures that the party offering the option cannot renege, and the party purchasing the option provides fair compensation (in the form of a fee) to the offering party. We sketch the evolution of such protocols, starting with two-phase commit, and finishing with timed hashlocked smart contracts. 

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5. Refinement for Multiagent Information Protocols

   Christie V, Samuel H.; Chopra, Amit K.; Singh, Munindar P. (May 2020, Proceedings of the 19th International Conference on Autonomous Agents and MultiAgent Systems (AAMAS))

   An interaction protocol specifies a decentralized multiagent system operationally by specifying constraints on messages exchanged by its member agents. Engineering with protocols requires support for a notion of refinement, whereby a protocol may be substituted without loss of correctness by one that refines it. We identify two desiderata for refinement. One, generality: refinement should not restrict enactments by limiting protocols or infrastructures under consideration. Two, preservation: to facilitate modular verification, refinement should preserve liveness and safety. We contribute a novel formal notion of protocol refinement based on enactments. We demonstrate generality by tackling the declarative framework of information protocols. We demonstrate preservation by formally establishing that our notion of refinement is safety and liveness preserving. We show the practical benefits of refinement by implementing a checker. We demonstrate that it is less time-intensive to check refinement (and thereby gain safety and liveness) than to recheck safety and liveness of a composition. 

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