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Chapter 8 The nature of communication

Syntax-how structured Semantics-symbol meaning Pragmatics-interpretation. Chapter 8 The nature of communication. Human communication

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Chapter 8 The nature of communication

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  1. Syntax-how structured Semantics-symbol meaning Pragmatics-interpretation 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 communication SpeakerHearer  IntentionPerception Generation- createAnalysis Synthesis- organizeDisambiguation Incorporation 1

  2. Artificial Communication • low-level language vs high-level languages • direct communication vs. indirect communication Computer communication • shared memory message passing Agent communication/ MAS communication • Communication in MAS = more than simple communication, implies interaction • The environment provides a computational infrastructure • protocols for agents to communicate • protocols for agents to interact 2

  3. 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: • coordinate their actions and behavior • attempt to change state of the other agents • attempt to get other agents perform actions 3

  4. 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

  5. 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 states Pragmatics: 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

  6. Reactive agents 2. Indirect communication 2.1 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 2.2 Trails- L. Steels, 1995 agents drop "radioactive crumbs" making trails an agent following a trail makes the trail faint until it disappears 6

  7. Cognitive agents Control KS KS KS KS 2.3Blackboard 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) events Blackboard Pending KS Activations 7

  8. 3. Direct communication Sending messages = method invocation • Exchange of partial plans • distributed planning ACL = Agent Communication Languages communication as action - communicative acts 8

  9. ACL Content language Ontology 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 9

  10. 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)

  11. Origins 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.

  12. Theory of Speech Acts J. Austin - How to do things with words, 1962, J. Searle - Speech acts, 1969 Treats communication as an action – made to further agent’s intentions Changes world in a way analogous to physical actions Need 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 pleaseclose the door“ desire illocution Effect perlocution specific words -locution 12

  13. 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.

  14. 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

  15. Speech Acts Components • In general, speech acts can be seen to have 2 components: • A performative verb • e.g. Request, inform • Propositional content • e.g. ”the window is closed”

  16. Content (Message itself) Content Communication Message KQML – Knowledge Query and Manipulation Language A 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 Core of KQML - identity of the network protocol with which to deliver the message - speech act or performative Optional - content language - ontology Describes low level communication parameters: - identity of sender and receiver - a unique id associated with the communication 16

  17. 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.

  18. 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.

  19. 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))

  20. Communication Mechanics of communication, e.g. Sender, receiver. Performatives (message layer) Logic of communication, e.g. ask, tell. Content Content of communication, e.g. a KIF expression KQML • An “outer language” that defines a set of performatives (communicative acts), such as ask, reply. • Ontology specifies which namespace to use. e.g. (ask-if :sender agenti :receiver agentj :language Prolog :ontology genealogy :content “spouse(adam, eve)”)

  21. KQML - Performatives • 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.

  22. KQML Categories of Performatives

  23. ask-all(P) tell(P1,P2,...) (tell :sender willie :receiver joe :reply-with block1 :language KIF :ontology BlockWorld :content (AND (Block A)(Block B) (On A B)) ) 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) ) 1. Query performatives: ask-one, ask-all (want all answers to question), ask-if, stream-all (multiple response version of ask-all) A ask-one(P) B tell(P) (stream-all :sender willie :receiver ibm-stock :content (price ?VL ?price ) ) (standby :content (stream-all :content (price ?VL ?price) ) A B stream-all(P) B tell(P1) A tell(P2) eos 23

  24. insert(P) delete(P) tell(P) untell(P) 2. Generator performatives: standby (be ready to respond), ready, next, rest, discard, generate,... 3. Response performatives: reply, sorry ... B A 4. Generic informational performatives: tell (I know it), untell, insert (add to your VKB), delete, ... 5. Capability performatives: advertise, subscribe, recommend... A B 6. Network performatives: register, unregister, forward, route, ... Facilitator 24

  25. 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))

  26. 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

  27. 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

  28. (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)

  29. 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

  30. F tell(X) ask(X) A B Facilitators Point-to-point protocol A is aware that it is appropriate to send a query about X toB There are several ways to achieve this via a Facilitator.

  31. Facilitators 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. tell(X) subscribe(ask(X)) F tell(X) A B

  32. advertise(ask(X)) broker(ask(X)) tell(X ) F tell(X ask(X) ) A B Facilitators Using the broker performative A asks Facilitator to find another agent which can process a given performative.

  33. advertise(ask(X)) recruit(tell(X)) F ask(X) tell(X ) A B Facilitators 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.

  34. recommend(ask(X)) advertise(ask(X)) reply(B) F ask(X) A B tell(X) Facilitators Using the recommend performative Asks Facilitator to respond with the ”name” of another agent which is appropriate for sending a particular performative.

  35. 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 hoc Resulted in FIPA

  36. 3.3 FIPA- ACL Foundation for Intelligent Physical Agents, 1996 Goal of FIPA = make available specifications that maximize interoperability across agent-based systems. SL formal language Syntax 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 acts Informatives - query_if, subscribe, inform, inform_if confirm, disconfirm, not_understood Task distribution - request, request_whenever, cancel, agree, refuse, failure Negotiation - cfp (call for proposal - initiate), propose, accept_proposal, reject_proposal 36

  37. FIPA - Semantics SL (Semantic Language) - a quantified, multi-modal logic, with modal operators: B - belief D - desire U - 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 about Bif - 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. 37

  38. 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 

  39. Syntax of request: <k, request(j, )> Pre: BkAgent( ,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.

  40. Using ACLs in MAS Any MAS that is to use an ACL must provide: • a finite set of APIs for composition, sending, and receiving ACL messages • an 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 40

  41. ACL Content language Ontology 4. Communication content • Content languages • KIF • Prolog • Clips • SQL • FIPA-SL, FIPA-CCL, FIPA-KIF • DAML • XML Xtensible Markup Language • Ontologies DARPA Agent Markup Language The DAML Program officially began in August 2000. The goal of the DAML effort is to develop a language and tools to facilitate the concept of the Semantic Web. 41

  42. Interaction protocols enable agents to have conversations, i.e., structured exchanges of messages • Finite automata • Conversations in KQML • Petri nets - more in distributed planning lecture • FIPA IP standards: • FIPA-query,FIPA-request,FIPA-contract-net,

  43. Finite state automataNodes represent statesArrows represent actions COOL, Barbuceanu,95 A:B<<ask(do P) B:A<<accept(do P) proposeS(P) B:A<<refuse(do P) acceptR(P) rejectR(P) B:A<<fail(do P) B:A<<result(do P) counterR(P) counterS(P) Winograd, Flores, 1986 rejectS(P) acceptS(P) 43

  44. Conversations in KQML Use Definite Clause Grammars (DCG) formalism for the specification of conversation policies for KQML performatives DCGs extend Context Free Grammars in the following way: • non-terminals may be compound terms • the 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 44

  45. DA BR AR1 DB AR2 Petri nets Ferber, 1997 Petri 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. B does not want to do(P) A wants to do P, A cannot do P B is willing to do(P) Request do(P) Refuse do(P) Accept/request do(P) Completed(P) Fail to do(P) Impossible to do(P) Notification of end(P) FB FA1 45 Failure FA2 Satisfaction

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