Download Multiagent System and S0cieties of Agents

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
Outline
1. Introduction
2. Agent communications
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Coordination
Dimensions of meaning
Message types
Communication levels
Speech acts, KQML, KIF, Ontology, other
3. Agent interaction protocols
4. Societies of agents
5. Conclusions
Introduction
How to analyze, describe, and design environments in
which agents can operate effectively and interact
with each other productively.
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Communication protocols
[Xu Lin]
Enable agents to exchange and understand messages
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Interaction protocols
[Shabbir Syed]
Enable agents to have conversations, which are structured
exchanges of messages
Communication protocols
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Enable agents to exchange and understand
messages
The messages can be exchanged between
two agents:
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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
Interaction protocols
Enable agents to have conversations,
which are structured exchanges of
messages
Negotiation can occur between Agent1
and Agent2
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Agent1 proposes a course of action to Agent2
Agent2 evaluates the proposal and
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Sends
Sends
Sends
Sends
acceptance to Agent1 or
counterproposal to Agent1 or
disagreement to Agent1 or
rejection to Agent1
Motivation
Centralized solutions are generally more efficient,
why should we interested in distribution system?
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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
Characteristics of Multiagent
Environments
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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
Agent Communications
An agent is an active object with the ability
to perceive, reason, and act
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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)
Communications
1.
2.
3.
4.
5.
Coordination
Dimensions of meaning
Message types
Communication levels
Examples:
a. Speech acts
b. KQML
c. KIF
d. Ontologies
e. Other…
Coordination
A property of a system of agents performing
some activity in a shared environment
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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
Ways for coordinating behavior and
activities among agents
How well a system behaves as a unit?
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How it can maintain global coherence without
explicit global control
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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
Dimensions of meaning
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Three aspects to the formal study of communication:
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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
Different dimensions of meaning
associated with communication
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Descriptive vs. Prescriptive
Personal vs. Conventional meaning
Subjective vs. Objective meaning
Speaker’s vs. Hearers’s vs. Society’s Perspective
Semantics vs. Pragmatics
Contextually
Coverage
Identity
Cardinality
Message types
Two basic message types: assertions and queries
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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
Message types
Two basic message types:
assertions and queries
Dialogue vs.
Active
Passive
Both
Function
Master
Slave
Both
Communication levels
Communication protocols are typically specified at
several levels:
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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.
Communication levels (cont’d)
There are both binary and n-ary communication protocols:
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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:
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Sender
Receiver(s)
Language in the protocol
Encoding and decoding functions
Actions to be taken by the receiver(s)
Speech Act (I)
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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
Speech Act (II)
A speech act has three aspects:
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Locution: the physical utterance by the speaker.
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Illocution: the intended meaning of the utterance by
the speaker.
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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
Knowledge Query and Manipulation
Language (KQML)
[Finin 94]
KQML is a protocol for exchanging information and
knowledge.
The basic KQML
Information for understanding the content of the message
is includes in the communication itself
(KQML-performative
:sender
:receiver
:language
:ontology
:content
…)
Syntax is Lisp-like :--)
<word>
<word>
<word>
<word>
<expression>
Nested KQML message
Seven basic categories of KQML
1.
2.
3.
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5.
6.
7.
Basic query performatives
Multiresponse query performatives
Response performatives
Generic informational performatives
Generator performatives
Capability-definition performatives
Networking performatives
Issues
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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]
Knowledge Interchange Format (KIF)
[Genesereth?]
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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.
Ontologies
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[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
Other communication protocols
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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
Questions?
If not, let’s start the discussion