Chapter 8 The nature of communication Human communication Communication is the intentional exchange...
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Transcript of Chapter 8 The nature of communication Human communication Communication is the intentional exchange...
Chapter 8 The nature of communication
Human communication Communication is the intentional exchange of information brought about
by the production and perception of signs drawn from a shared system of conventional signs (AIMA, Russell&Norvig) language
Communication seen as an action (communicative act) and as an intentional stance (want something to happen)
Component steps of communicationSpeaker Hearer Intention Perception Generation- create Analysis Synthesis- organize Disambiguation
Incorporation
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Syntax-how structuredSemantics-symbol meaningPragmatics-interpretation
Artificial Communication low-level language vs high-level languages direct communication vs. indirect communication
Computer communication shared memory message passing
Agent communication/ MAS communicationCommunication in MAS = more than simple
communication, implies interactionThe environment provides a computational
infrastructure protocols for agents to communicate protocols for agents to interact
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Communication protocols = enables agents to exchange and understand messages
Interaction protocols = enable agents to have conversations, i.e., structured exchanges of messages. Can trace series of responses.
Aim Communication enables agents to:
o coordinate their actions and behavior
o attempt to change state of the other agents
o attempt to get other agents perform actions
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Communication infrastructure • blackboard (shared memory) or message-based• connected or connection-less (email) • point-to-point (1), multicast (some), broadcast (all)
• push or pull (information given to you or requested)
• synchronous or asynchronous
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Dimensions of Meaning(think of examples of each)
• Descriptive/Prescriptive: describe phenomenon vs proscribe behavior (I am cold)
• Personal/conventional: different meaning to individual
• Semantics/Pragmatics: interpreted differently than intended: mental statesPragmatics: the study of how people use language. How
people comprehend and produce communication.• Contextuality: cannot be understood in isolation• Coverage: language express necessary concepts• Identity: meaning is dependent on individual• Cardinality: private message interpreted
differently than public message
2. Indirect communication2.1 Signal propagation (no specific target) - Manta, A. Drogoul 1993 An agent sends a signal, which is broadcast into the environment, and
whose intensity decreases as the distance increases At a point x, the signal may have one of the following intensities (why?)• Topological differences lead to social differences
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2.2 Trails - L. Steels, 1995agents drop "radioactive crumbs" making trailsan agent following a trail makes the trail faint until it disappears
Reactive agentsReactive agents
2.3 Blackboard systems, Barbara Hayes-Roth, 1985
Blackboard = a common area (shared memory) in which agents can exchange information, data, knowledge
Agents initiates communication by writing info on the blackboard Agents are looking for new info, they may filter it Agents must register with a central site for access authorization Blackboard = a powerful distributed knowledge paradigm Agents = Knowledge sources (KS)
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Cognitive agentsCognitive agents
KS
KS
KS
KS
Control
Blackboard
events
Pending KS Activations
3. Direct communication
Sending messages = method invocationExchange of partial plans
– distributed planning
ACL = Agent Communication Languages
communication as action - communicative acts
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3.1 Agent Communication Languages Concepts (distinguish ACLs from other means of communication such as
RPC, RMI or CORBA, ORB – in which a procedure is remotely called): ACLs handle propositions, rules, and actions instead of objects with no
associated semantics An ACL message describes a desired state in a declarative language, rather
than a procedure or method invocation ACLs are mainly based on BDI theories: BDI agents attempt to
communicate their BDI states or attempt to alter others BDI state ACLs are based on Speech Act Theory Agent behavior and strategy drive
communication and lead to conversations
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ACL
Content language
Ontology
Ontology =formal definition of a body of knowledge. The most typical ontology used in building agents involves a structural component. Essentially a taxonomy of class and subclass relations coupled with definitions and relationships between things. (Jim Hendler)
An ontology is analogous to a data base organization, not the contents of the database.
Example: To express the idea that a block is a physical object we might use the first order predicate language expression:
x (Block x) (PhysicalObject x)To state relationships between classes:x,y,z (instanceOf x y ) (subclassOf y z) (instanceOf x z)To define a relationship On(X,Y) (domain On PhysicalObject) (range On PhysicalObject)
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Origins of ACLsOrigins of ACLs
Knowledge Sharing Effort - DARPA, 1990 External Interface Group - interaction between KBS - KQML Interlingua – language for communicating between independent
agents. KIF (not designed as a language to be used by humans) Shared, Reusable Knowledge Bases – Ontolingua (set of tools written in Lisp for analyzing and
translating ontologies. Uses KIF parser and syntax checker. Resulted in
(Web-based) KQML: Knowledge Query and Manipulation Language
• Language for both message formatting and message handling protocols.
KIF: Knowledge Interchange Format
• Langauge for expressing message content.
Theory of Speech ActsJ. Austin - How to do things with words, 1962,
J. Searle - Speech acts, 1969Treats communication as an action – made to further agent’s intentionsChanges world in a way analogous to physical actionsNeed formal representation so planning systems can reason about
them.
A speech act has 3 aspects: locution = physical utterance by the speaker illocution = the intended meaning of the utterance by the speaker
(performative) prelocution = the action that results from the locution
Alice told Tom: "Would you please close the door“
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desireillocution
Effect perlocutionspecific words -locution
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Human Communication: Intent may be ambiguous
• Colleague states “I am cold”
• What is the meaning?
• For computers, state performative (KQML) or Communicative Act (FIPA) so no ambiguity (except in content itself).
• Note, FIPA is an improvement over KQML, but has same goal.
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Illocutionary aspect - several categories(According to speech act theory)
Assertives, which inform: the door is shut Directives, which request: shut the door, Commissives, which promise something: I will shut the door Permissive, which gives permission for an act: you may shut the
door Prohibitives, which ban some act: do not shut the door Declaratives, which causes events: I name you king of Cache
Valley; You are not guilty. Expressives, which express emotions and evaluations: I am happy Excuse me, congratulations
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Speech Act Please close the door
The door is closed Is the door closed?
Performative request inform inquire
Content the door is closed the door is closed the door is closed
Speech Acts Components
• In general, speech acts can be seen to have 2 components:
1. A performative verb
• e.g. Request, inform
2. Propositional content
• e.g. ”the window is closed”
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KQML – Knowledge Query and Manipulation LanguageA high-level, message-oriented communication language and protocol for information exchange, independent of content syntax (KIF, SQL, Prolog,…) and application ontology
KQML separates: semantics of the communication protocol (domain independent) semantics of the message (domain dependent)
3 (conceptual) layers
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Content (Message itself)Content
Communication
Message
Describes low levelcommunication parameters:- identity of sender and receiver- a unique id associated with the communication
Core of KQML- identity of the network protocol with which to deliver the message- speech act or performative Optional- content language- ontology
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KIF (Knowledge Interchange Format)
• Motivation: creation of a common language for
expressing properties of a domain.
– Intented to express contents of a message; not the
message itself.
– Based on first-order logic.
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• Using KIF (think in terms of Lisp type statements), it’s
possible to express:
– Properties of things in a domain
• e.g. Michael is a vegetarian – Michael has the property of being a
vegetarian
– Relationships between things in a domain
• e.g. Michael and Janine are married – the relationship of marriage
exists between Michael and Janine.
– General properties of a domain
• e.g. Everybody has a mother.
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KIF - Example
• Relation between 2 objects:
– The temperature of m1 is 83 Celsius:
(= (temperature m1) (scalar 83 Celsius))
• Definition of new concept:
– An object is a bachelor if this object is a man and not married:(defrelation bachelor (?x) :=
(and (man ?x)
(not (married ?x))))
• Relationship between individuals in the domain:
– A person with the property of being a person also has the property of
being a mammal:
(defrelation (person ?x) :=> (mammal ?X))
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• An “outer language” that defines a set of performatives (communicative acts), such as ask, reply.
• Ontology specifies which namespace to use.
CommunicationMechanics of communication, e.g. Sender, receiver.
Performatives (message layer)
Content of communication,e.g. a KIF expression
Content
Logic of communication, e.g. ask, tell.
e.g.
(ask-if :sender agenti
:receiver agentj
:language Prolog
:ontology genealogy
:content “spouse(adam, eve)”)
KQML
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• The idea of communication in KQML is to represent
illocutionary (meaning) acts.
• Performatives form the core of the language:
– Determine the kinds of interactions one can have with KQML-
speaking agents.
– Identify the protocol to be used to deliver the message
– Signify that the content is an assertion, a query, a command or
another speech act.
– Describe how the sender would like any reply to be delivered.
KQML - Performatives
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KQML Categories of Performatives
Category Performatives
Basic Query evaluate, ask-if, ask-one, ask-all, ask-about
Multi-response Query stream-about, stream-all
Response reply, sorry
Generic informational tell, achieve, cancel, untell
Generator standby, ready, next,rest, discard, generator
Capability-definition advertise, subscribe, monitor, import, export
Networking register, unregister, forward, broadcast, route
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Syntax LISP-like list of attribute/value pairs
(ask-one :sender joe :receiver ibm-stock :reply-with ibm-stock :language PROLOG // of content :ontology NYSE-TICKS // define terminology :content (price ibm ?price) )
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(tell :sender willie:receiver joe:reply-with block1:language KIF:ontology BlockWorld:content (AND (Block A)(Block B)
(On A B)) )1. Query performatives: ask-one, ask-all (want all answers to question), ask-if, stream-all (multiple response version of ask-all)
(stream-all :sender willie:receiver ibm-stock:content (price ?VL ?price ) )
(standby:content (stream-all:content (price ?VL ?price) )
ask-one(P)
tell(P)
tell(P1)
stream-all(P)
tell(P2)eos
tell(P1,P2,...)
ask-all(P)
B
B
B
A
A
A
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4. Generic informational performatives:
tell (I know it), untell, insert (add to your VKB), delete, ...
tell(P)
untell(P)
delete(P)
insert(P)
2. Generator performatives:standby (be ready to respond), ready, next, rest, discard, generate,...
6. Network performatives:register, unregister, forward, route, ...
3. Response performatives:reply, sorry ...
5. Capability performatives:advertise, subscribe, recommend...
Facilitator
A
A
B
B
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Example of KQML Dialog(evaluate :sender A :receiver B :language
KIF :ontology motors
:reply-with q1
:content (val (torque m1))
(reply
:sender B :receiver A :language KIF
:ontology motors :in-reply-to q1
:content (= (torque m1) (scalar 12 kgf))
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Another example of KQML
(stream-about // multiple responses wanted
:sender A :receiver B :language KIF :ontology motors
:reply-with q1 :content m1)
(tell :sender B :receiver A :in-reply-to q1
:content (=(torque m1) (scalar 12 kgf))
(tell :sender B :receiver A :in=reply-to q1
:content (= (status m1) normal))
(eos :sender B :receiver B :in-reply-to q1) //end of stream
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In the next KQML example
• A advertises that it is willing to accept subscriptions related to m1.
• B responds by subscribing
• A sends message sequence about m1
• A untells the previous fact and gives new information
• eos ends the stream of messages
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(advertise :sender A :language KQML :ontology K10:content (stream-about :language KIF :ontology motors :content m1)))(subscribe :sender B :receiver A :reply-with s1:content (stream-about :language KIF :ontology motors : content m1))(tell :sender A :receiver B :in-reply-to s1 :content (=(torque m1)(scalar 12 kgf)))(tell :sender A :receiver B :in-reply-to s1 :content (=(status m1) normal))(untell :sender A :receiver B :in-reply-to s1 :content (=(torque m1)(scalar 12 kgf)))(tell :sender A :receiver B :in-reply-to s1 :content (=(torque m1)(scalar 15 kgf)))(eos :sender A :receiver B :in-reply-to s1)
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Facilitators • KQML environments (may) contain facilitators that help
make the communication protocol transparent.
• Facilitators: a special class of agents that perform useful
communication services such as:
– Maintain registry of service names
– Forward messages to named services
– Routing messages based on content
– Provide matchmaking between information providers and seekers
– Provide mediation and translation services
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A B
F
ask(X)
tell(X)
Facilitators
Point-to-point protocol
A is aware that it is appropriate
to send a query about X to B
There are several ways to achieve
this via a Facilitator.
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A B
Ftell(X)
subscribe(ask(X)) tell(X) Using the subscribe performative
Request that Facilitator F monitor
for the truth of X. If B subsequently
informs F that it believes X to be
true, then F can in turn inform A.
Facilitators
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A B
Ftell(X) ask(X)
broker(ask(X))
advertise(ask(X))
tell(X)Using the broker performative
A asks Facilitator to find another agent
which can process a given performative.
Facilitators
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A B
Fask(X)
recruit(tell(X))
advertise(ask(X))
tell(X)
Using the rercruit performative
A asks Facilitator to find an appropriate
agent to which an embedded
performative can be forwarded. A reply
is returned directly to the original agent.
Facilitators
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A B
Freply(B)
ask(X)
tell(X)
recommend(ask(X)) advertise(ask(X))
Using the recommend performative
Asks Facilitator to respond with the ”name”
of another agent which is appropriate for
sending a particular performative.
Facilitators
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Criticisms of KQML
• not fixed performatives – different implementations don’t interoperate
• transport mechanisms (ways of getting a message from A to B) not precisely defined
• semantics not rigorous – not adhered to• missing commissives (make commitment)• performative set too large and ad hocResulted in FIPA
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3.3 FIPA - ACLFoundation for Intelligent Physical Agents, 1996
Goal of FIPA = make available specifications that maximize interoperability across agent-based systems. SL formal languageSyntax similar to KQML(inform :sender Agent1
:receiver Agent2 :content (price good2150)
:in-reply-to round-1: reply-with bid03: language S1:ontology hp-auction:reply-by 10:protocol offer:conversation-id conv-1 )
FIPA communicative actsInformatives - query_if, subscribe, inform, inform_ifconfirm, disconfirm, not_understoodTask distribution - request, request_whenever, cancel, agree,refuse, failureNegotiation - cfp (call for proposal - initiate), propose, accept_proposal, reject_proposal
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FIPA - SemanticsSL (Semantic Language) - a quantified, multi-modal logic, with modal operators:B - beliefD - desireU - uncertain belief – neither believes or its negation, but believes more likely than its negation.PG - persistent goal, but will not necessarily plan to bring it aboutBif - agent believes or disbelieves Uif - agent has an uncertain belief of or an uncertain belief of ¬
Given that one of the most frequent and serious criticisms of KQML is the lack of adequate semantics, it is not surprising that the developers of FIPA felt it important to give comprehensive formal semantics to their language.
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The semantics of a communicative act is specified as a set of SL's formulae that describe:
Feasibility preconditions - the necessary conditions for the sender - the sender is not obliged to perform the CA
Rational effect - the effect that an agent can expect as a result of performing the action; it also typically specifies conditions that should hold true of the recipient
The receiving agent is not required to ensure that the expected effect comes about
The sender can not assume that the rational effect will necessary follow
Semantics of inform:
<i, inform(j, )>
Pre: Bi Bi (Bifj Uifj )
Post: Bj
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Syntax of request:
<k, request(j, )>
Pre: Bk Agent( ,j) BkIj(Done )
Post: Done()
Agent( ,j) means that the agent of action is j (j is the one who can perform the action)
Done( ) means that the action has been done
Effect: agent k is requesting agent j to do action and agent k believes that the agent to do the action is j and it believes that j does not currently intend to do the action. The effect is that j will do it.
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Using ACLs in MASAny MAS that is to use an ACL must provide:a finite set of APIs for composition, sending, and receiving ACL messagesan infrastructure of services that assist agents in naming, registration, and basic facilitation services (finding other agents that can do things for your agent)code for every reserved message type that takes the action prescribed by the semantics for the particular application;the code depends on the application language, the domain, and the details of the agent system using the ACL
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4. Communication content
Content languages– KIF– Prolog– Clips– SQL– FIPA-SL, FIPA-CCL, FIPA-KIF– DAML– XML Xtensible Markup Language
Ontologies
ACL
Content language
Ontology
DARPA Agent Markup LanguageThe DAML Program officially began in August 2000.The goal of the DAML effort is to develop a languageand tools to facilitate the concept of the Semantic Web.
Interaction protocols
enable agents to have conversations, i.e., structured exchanges of messages
Finite automataConversations in KQMLPetri nets - more in distributed planning lecture
FIPA IP standards:– FIPA-query, FIPA-request, FIPA-contract-net,
Finite state automataNodes represent states
Arrows represent actions
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A:B<<ask(do P)
B:A<<accept(do P)
B:A<<refuse(do P)
B:A<<result(do P)B:A<<fail(do P)
proposeS(P)
acceptR(P) rejectR(P)
counterR(P)counterS(P)
acceptS(P) rejectS(P)Winograd, Flores, 1986
COOL, Barbuceanu,95
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Conversations in KQMLUse Definite Clause Grammars (DCG) formalism for the specification of conversation policies for KQML performativesDCGs extend Context Free Grammars in the following way:non-terminals may be compound termsthe body of the rule may contain procedural attachments, written as "{" and "}" that express extra conditions that must be satisfied for the rule to be valid
Ex: noun(N) [W], {RootForm(W,N), is_noun(N)}
S s(Conv, P, S, R, inR, Rw, IO, Content), {member(P, [advertise, ask-if]}
s(Conv, ask-if, S, R, inR, Rw, IO, Content) [ask-if, S, R, inR, Rw, IO, Content] |[ask-if, S, R, inR, Rw, IO, Content], {OI is inv(IO)},
r(Conv, ask-if, S, R, _, Rw, OI, Content)
r(Conv, ask-if, R, S, _, inR, IO, Content) [tell, S, R, inR, Rw, IO, Content] |problem(Conv, R, S, inR, _, IO)
Labrou, Finin, 1998
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DAA wants to do P,A cannot do P
Request do(P)
Refuse do(P)
Accept/request do(P)
Fail to do(P)
Notification of end(P)
DB
AR1
AR2
FA2FA1
BR
FBFailure Satisfaction
Impossibleto do(P)
B does not wantto do(P)
B is willingto do(P)
Completed(P)
Petri netsPetri net = oriented graph with 2 type of nodes:places and transitions;there are moving tokens through the net - representation of dynamic aspect of processes. Stores state.Tokens are moved from place to place, following firing rules.A transition T is enabled if all the input places P of T contains a token A marking (state) is a distribution of tokens over places.
Ferber, 1997
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