1. 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

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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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)

9. Communications Coordination Dimensions of meaning Message types
Communication levels
Examples:
Speech acts
KQML
KIF
Ontologies
Other…

10. 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

11. Ways for coordinating behavior and activities among agents

12. 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

13. 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

14. Different dimensions of meaning associated with communication
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

15. 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

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

17. 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.

18. Communication levels (cont’d)
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)

19. 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

20. 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

21. Knowledge Query and Manipulation Language (KQML) [Finin 94]
KQML is a protocol for exchanging information and knowledge.

22. The basic KQML
Information for understanding the content of the message is includes in the communication itself
(KQML-performative
:sender <word>
:receiver <word>
:language <word>
:ontology <word>
:content <expression> …)
Syntax is Lisp-like :--)

23. Nested KQML message

24. Seven basic categories of KQML
Basic query performatives
Multiresponse query performatives
Response performatives
Generic informational performatives
Generator performatives
Capability-definition performatives
Networking performatives

25. 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]

26. 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.

27. 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

28. 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

29. Questions? If not, let’s start the discussion