In computer science , the Actor model , first published in 1973 ( Hewitt et al., 1973 ), is a mathematical model of concurrent computation . This article reports on the latest history of the Actor model in which major themes have been investigated in the study of the model, study of issues of composition, development of architectures, and application to Open systems. It is the follow on article to Actor model middle history which reports on the initial implementations, initial applications, and development of the first proof theory and denotational model.
Power of the Actor Model
Investigations began in the basic power of the Actor model. Carl Hewitt  argued That Because of the use of Arbiters que la Actor model Was More Powerful than logic programming (see indeterminacy in concurrent computation).
A family of Prolog -like competitor message passing systems using Keith Clark , Herve Gallaire, Steve Gregory, Vijay Saraswat, Udi Shapiro, Kazunori Ueda, etc.Some of these authors made claims that these systems were based on mathematical logic. However, the Actor model, the Prolog-like competitor systems, were based on the message that they are subject to indeterminacy in the ordering of messages that are similar to the indeterminacy of arrival of messages sent to the Actors. Carl Hewitt and Gul Agha  concluded that the Prolog-like competitor systems were neither deductive nor logical. They were not deductive because computational steps were not necessarily deduced from their predecessors and they were not logical because of their ability to derive the results of subsequent computational situations from their predecessors
Compositionality concerns composing systems from subsystems. Issues of Compositionality HAD proven to be serious limitations for previous theories of computation Including the lambda calculus and Petri nets . Eg, two lambda expressions are not a lambda expression and two net petri are not a net petri and can not influence each other.
In his doctoral dissertation Gul Agha addressed issues of compositionality in the Actor model. Actor configurations have receptionists that can receive messages from other locations. In this way two Actor configurations can be made into another configuration whose subconfigurations can communicate with each other. Actor’s configurations have the advantage that they can have multiple Actors ( ie the receptionists) which receive messages from multiple sources (see issues with getting messages from multiple channels ).
Carl Hewitt  pointed out that openness has become a fundamental challenge in software system development. Open distributed systems are required to meet the following challenges:
- Once something is published in an open distributed system, it can not be taken back.
- Different subsystems of an open distributed system include heterogeneous, overlapping and possibly conflicting information. There is no central arbiter of truth in open distributed systems.
- Unbounded nondeterminism
- Asynchronously, different subsystems can come up and go down and communication links. Therefore the time that it will take to complete an operation can not be bound in in advance (see unbounded nondeterminism ).
- Large distributed systems are inevitably inconsistent regarding their information about the information system interactions of their human users
Carl Hewitt and Jeff Inman  worked on developing semantics for Open Systems to address issues in the field of distributed artificial intelligence. Carl Hewitt and Carl Manning  reported on the development of Participatory Semantics for Open Systems.
Researchers at Caltech under the leadership of Chuck Seitz developed the Cosmic Cube which was one of the first message-passing Actor architectures. Subsequently at MIT researchers under the leadership of Bill Dally developed the J Machine .
Attempts to Relate Actor Semantics to Algebra and Linear Logic
Kohei Honda and Mario Tokoro 1991, Jose Meseguer 1992, Ugo Montanari and Carolyn Talcott 1998, Gaspari M. and G. Zavattaro 1999. Also John Darlington and YK Guo, 1994, have attempted to relate linear logic to Actor semantics.
However, none of the above formalisms addresses the crucial property of guarantee of service (see unbounded nondeterminism ).
Recent developments in the Actor model have come from several sources.
Hardware development is furthering local and nonlocal massive concurrency. Local concurrency is being enabled by new hardware for 64-bit many-core microprocessors, multi-chip modules, and high performance interconnect. Nonlocal concurrency est disponible en ligne de la machine dÃ © lÃ © gÃ © nÃ © nÃ © e de la machine dÃ © lÃ © gÃ © nÃ © e de wireless network broadband packet switched communications Both local and nonlocal storage capacities are growing exponentially. These hardware developments pose enormous modeling challenges. Hewitt [Hewitt 2006a, 2006b] is attempting to use the Actor model to address these challenges.
- Carl Hewitt; Peter Bishop and Richard Steiger (1973). “A Universal Modular Actor Formalism for Artificial Intelligence”. IJCAI.
- Carl Hewitt. The Challenge of Open Systems Byte Magazine. April 1985. Reprinted in The foundation of artificial intelligence — a sourcebook Cambridge University Press. 1990.
- Agha, Gul (1986), Actors: A Model of Competitive Computing in Distributed Systems (Doctoral Dissertation) , MIT Press
- Carl Manning. Traveler: the actor observatory ECOOP 1987. Also appears in Lecture Notes in Computer Science , vol. 276.
- William Athas and Charles Seitz Multicomputers: message-passing concurrent computers IEEE Computer August 1988.
- William Dally and Wills, D. Universal mechanisms for concurrency PARLE 1989.
- W. Horwat, A. Chien, and W. Dally. Experience with CST: Programming and Implementation PLDI. 1989.
- Carl Hewitt. Towards Open Information Systems Semantics Proceedings of International Workshop on Distributed Artificial Intelligence. October 23-27, 1990. Bandera, Texas.
- Akinori Yonezawa , Ed. ABCL: An Object-Oriented Concurrent MIT Press System . 1990.
- K. Kahn and Vijay A. Saraswat, ” Actors as a Special Case of Competitor Constraint (Logic) Programming “, in SIGPLAN Notices , October 1990. Describes Janus .
- Carl Hewitt. Semantics Open Information Systems Journal of Artificial Intelligence. January 1991.
- Carl Hewitt and Jeff Inman. DAI Betwixt and Between: From Intelligent Agents to Open Systems Science IEEE Transactions on Systems, Man, and Cybernetics. November / December 1991.
- Carl Hewitt and Gul Agha. Guarded Horn clause languages: are they deductive and logical? International Conference on Fifth Generation Computer Systems, Ohmsha 1988. Tokyo. Also in Artificial Intelligence at MIT , Vol. 2. MIT Press 1991.
- Kohei Honda and Mario Tokoro. An Object Calculus for Asynchronous Communication ECOOP 91.
- José Meseguer. Conditional rewriting logic has a unified model of concurrency in Selected Papers of the Second Workshop on Concurrency and Compositionality. 1992.
- William Dally, et al. The Message-Driven Processor: A Multicomputer Processing Node with Efficient Mechanisms IEEE Micro . April 1992.
- S. Miriyala, G. Agha, and Y.Sami. Visulatizing actor programs using net predicate transition Journal of Visual Programming. 1992.
- – Gul Agha, Ian Mason, Scott Smith, and Carolyn Talcott:A Foundation for Actor ComputationJournal of Functional Programming January 1993.
- Carl Hewitt and Carl Manning. Negotiation Architecture for Large-Scale Crisis Management AAAI-94 Workshop on Conflict Management in Cooperative Problem Solving. Seattle, WA. August 4, 1994.
- – John Darlington and YK Guo:Formalizing Actors in the Linear LogicInternational Conference on Object-Oriented Information Systems. Springer-Verlag. 1994.
- Carl Hewitt and Carl Manning. Synthetic Infrastructure for Multi-Agency Systems Proceedings of ICMAS ’96. Kyoto, Japan. December 8-13, 1996.
- S. Frolund. Coordinating Distributed Objects: An Actor-Based Approach for Synchronization MIT Press. November 1996.
- W. Kim. ThAL: An Actor System for Efficient and Scalable Computing Computing PhD thesis. University of Illinois at Urbana Champaign. 1997.
- – Mauro Gaspari and Gianluigi Zavattaro:An Algebra of Actors, Technical Report UBLCS-97-4, University of Bologna, May 1997
- Ugo Montanari and Carolyn Talcott. Can Actors and Pi-Agents Live Together? Electronic Notes in Theoretical Computer Science. 1998.
- – M. Gaspari and G. Zavattaro:An Algebra of ActorsFormal Methods for Open Object Based Systems, 1999.
- N. Jamali, P. Thati, and G. Agha. An actor based architecture for customizing and controlling agent sets IEEE Intelligent Systems. 14 (2). 1999.
- Thati, R. Ziaei, and G. Agha. A Theory of May Testing for Actors Formal Methods for Open Object-based Distributed Systems. March 2002.
- Thati, R. Ziaei, and G. Agha. A Theory of May for testing asynchronous calculi with locality and no name matching Algebraic Methodology and Software Technology. Springer Verlag. September 2002. LNCS 2422.
- – Gul Agha and Prasanna Thati. An Algebraic Theory of Actors and Its Application to a Simple Object-Based Language, From OO to FM (Dahl Festschrift) LNCS 2635. Springer-Verlag. 2004.
- Carl Hewitt. The repeated demise of logic programming and why it will be reincarnated What Went Wrong and Why: Lessons from AI Research and Applications. Technical Report SS-06-08. AAAI Press. March 2006b.
- Carl Hewitt What is Commitment? Physical, Organizational, and Social COIN @ AAMAS. 2006a.