Multiagent Systems and Societies of Agents

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Multiagent Systems and Societies of Agents

• Authors Michael N. Huhns and Larry M. Stephens
• Speaker Lin Xu (part I) and Shabbir Syed (part
  II)
• CSCE 976, April 3rd 2002

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Outline

• Introduction
• Agent communications
• Coordination
• Dimensions of meaning
• Message types
• Communication levels
• Speech acts, KQML, KIF, Ontology, other
• Agent interaction protocols
• Societies of agents
• Conclusions

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Introduction

• How to analyze, describe, and design environments
  in which agents can operate effectively and
  interact with each other productively.
• Communication protocols
  Xu Lin
• Enable agents to exchange and understand
  messages
• Interaction protocols
  Shabbir Syed
• Enable agents to have conversations, which
  are structured exchanges of messages

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Communication protocols

• Enable agents to exchange and understand messages
• The messages can be exchanged between two agents
• Propose a course of action
• Accept a course of action
• Reject a course of action
• Retract a course of action
• Disagree with a proposed course of action
• Counter-propose a course of action

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Interaction protocols

• Enable agents to have conversations, which are
  structured exchanges of messages
• Negotiation can occur between Agent1 and Agent2
• Agent1 proposes a course of action to Agent2
• Agent2 evaluates the proposal and
• Sends acceptance to Agent1 or
• Sends counterproposal to Agent1 or
• Sends disagreement to Agent1 or
• Sends rejection to Agent1

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Motivation

• Centralized solutions are generally more
  efficient,
• why should we interested in distribution system?
• Easier to understand and easier to develop, when
  the problem being solved is itself distributed.
• Lead to computational algorithms that might not
  have been discovered with a centralized approach.
• A centralized approach is impossible.
• Respect real conditions privacy of agents,
  distribution

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Characteristics of Multiagent Environments

• Provide an infrastructure specifying
  communication and interaction protocols
• Typically open and have no centralized design
• Contain agents that are autonomous and
  distributed, and may be self-interested or
  cooperative

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Agent Communications

• An agent is an active object with the ability to
  perceive, reason, and act
• An agent has explicitly represented knowledge and
  a mechanism for operating on or drawing
  inferences from its knowledge
• An agent has the ability to communicate
  (receiving messages and sending messages)

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Communications

• Coordination
• Dimensions of meaning
• Message types
• Communication levels
• Examples
• Speech acts
• KQML
• KIF
• Ontologies
• Other

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Coordination

• A property of a system of agents performing
• some activity in a shared environment
• Avoid extraneous activity by reducing resource
  contention
• Avoid livelock and deadlock
• Maintain applicable safety conditions
• Cooperation Among non-antagonistic agents
• Negotiation Among competitive/self-interested
  agents

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Ways for coordinating behavior and activities
among agents
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How well a system behaves as a unit?

• How it can maintain global coherence without
  explicit global control
• Be able to determine on their own goals they
  share with other agents
• Determine common task
• Avoid unnecessary conflicts
• Pool knowledge and evidence
• Some organization among the agents is needed

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Dimensions of meaning

• Three aspects to the formal study of
  communication
• Syntax how the symbols of communication are
  structured
• Semantics what the symbol denote
• Pragmatics how the symbol are interpreted
• Meaning is a combination of semantics and
  pragmatics

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Different dimensions of meaning associated with
communication

• Descriptive vs. Prescriptive
• Personal vs. Conventional meaning
• Subjective vs. Objective meaning
• Speakers vs. Hearerss vs. Societys Perspective
• Semantics vs. Pragmatics
• Contextually
• Coverage
• Identity
• Cardinality

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Message types

• Two basic message types assertions and queries
• Basic agent accept assertions
• Passive role (answer questions) accept a query,
  send a reply, accept information
• Active role issue queries, make assertions,
  accept assertion
• Peer assume both active and passive role in
  dialog
  

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Message types

• Two basic message types
• assertions and queries
• Dialogue vs. Function
• Active Master
• Passive Slave
• Both Both

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Communication levels

• Communication protocols are typically specified
  at several levels
• Lowest level specifies the method of
  interconnection
• Middle level specifies the format, or syntax, of
  the information being transferred.
• Top level specifies the meaning, or semantics,
  of the information.

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Communication levels (contd)

• There are both binary and n-ary communication
  protocols
• Binary a single sender and a single receiver
• N-ary a single sender and multiple receivers
• A protocol is specified by a data structure with
  5 fields
• Sender
• Receiver(s)
• Language in the protocol
• Encoding and decoding functions
• Actions to be taken by the receiver(s)

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Speech Act (I)

• A popular basis for analyzing human communication
  is speech act theory
• Speech act theory views human natural language as
  actions
• Spoken human communication is used as the model
  for communication among computational agents

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Speech Act (II)

• A speech act has three aspects
• Locution the physical utterance by the speaker.
• Illocution the intended meaning of the utterance
  by the speaker.
• Perlocution the action that results from the
  locution.
• Speech act theory helps define the type of
  message
• by using the concept of illocutionary force,
  which
• constraints the semantics of the communication
  act itself

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Knowledge Query and Manipulation Language (KQML)
Finin 94

• KQML is a protocol for exchanging information and
  knowledge.

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The basic KQML

• Information for understanding the content of the
  message is includes in the communication itself
• (KQML-performative
• sender ltwordgt
• receiver ltwordgt
• language ltwordgt
• ontology ltwordgt
• content ltexpressiongt
• )
• Syntax is Lisp-like --)

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Nested KQML message
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Seven basic categories of KQML

1. Basic query performatives
2. Multiresponse query performatives
3. Response performatives
4. Generic informational performatives
5. Generator performatives
6. Capability-definition performatives
7. Networking performatives

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Issues

• The sender and receiver must understand the agent
  communication language
• The ontology must be created and be accessible to
  the agents that are communicating
• KQML must operate within a communication
  infrastructure that allows agents to locate each
  other
• KQML is still a work in progress and its
  semantics have not been completely defined
  1987

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Knowledge Interchange Format (KIF)
Genesereth?

• A logic language proposed as a standard to
  describe facts in expert systems, database,
  intelligent agents, etc.
• Specifically designed to serve as an
  interlingua or mediator in the translation of
  other languages
• KIF is a prefix version of first order predicate
  calculus with extensions to support non-monotonic
  reasoning and definitions. It also can be used to
  describe procedures.

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Ontologies Fikes et al.

• A specification of objects, concepts, and
  relationships in an area of interest
• The classes and relationships must be represented
  in the ontology
• An agent must represent its knowledge in the
  vocabulary of a specified ontology

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Other communication protocols

• Speech Act, KQML, KIF, Ontology in no way
  preclude other means by which agents can
  interact, communicate, and be interconnected
• Once communication protocols are defined and
  agreed upon by a set of agents, higher level
  protocols can be readily implemented
• ? Interaction Protocols

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Questions?If not, lets start the discussion