Agent Communication � In this lecture and the next, we cover LECTURE 8: macro-aspects of intelligent agent technology: those issues relating to the Agent Communication agent society , rather than the individual: � communication; speech acts; KQML & KIF; FIPA ACL � cooperation: An Introduction to MultiAgent Systems what is cooperation; prisoner’s dilemma; http://www.csc.liv.ac.uk/~mjw/pubs/imas cooperative versus non-cooperative encounters; the contract net 8-1 8-2 Speech Acts Speech Acts � Austin noticed that some utterances are rather � Most treatments of communication in (multi-) like ‘physical actions’ that appear to change the agent systems borrow their inspiration from state of the world speech act theory � Paradigm examples would be: � Speech act theories are pragmatic theories of � declaring war language, i.e., theories of language use: they � christening attempt to account for how language is used by � ‘I now pronounce you man and wife’ :-) people every day to achieve their goals and � But more generally, everything we utter is intentions uttered with the intention of satisfying some goal � The origin of speech act theories are usually or intention traced to Austin’s 1962 book, How to Do � A theory of how utterances are used to achieve Things with Words intentions is a speech act theory 8-3 8-4 Different Aspects of Speech Acts Different Aspects of Speech Acts � From “A Dictionary of Philosophical Terms � “ Illocutionary act: the speech act of doing and Names”: something else – offering advice or taking � “ Locutionary act: the simple speech act of a vow, for example – in the process of generating sounds that are linked together by uttering meaningful language. Thus, for grammatical conventions so as to say example, in saying ‘I will repay you this something meaningful. Among speakers of money next week,’ one typically performs English, for example, ‘It is raining’ performs the illocutionary act of making a promise.” the locutionary act of saying that it is raining, as ‘Grablistrod zetagflx dapu’ would not.” 8-5 8-6 1
Speech Acts Different Aspects of Speech Acts � Searle (1969) identified various different types of speech act: � “ Perlocutionary act: the speech act of � representatives: having an effect on those who hear a such as informin g, e.g., ‘It is raining’ meaningful utterance. By telling a ghost � directives: story late at night, for example, one may attempts to get the hearer to do something e.g., ‘please make the tea’ accomplish the cruel perlocutionary act � commisives: of frightening a child.” which commit the speaker to doing something, e.g., ‘I promise to… ’ � expressives: whereby a speaker expresses a mental state, e.g., ‘thank you!’ � declarations: such as declaring war or christening 8-7 8-8 Speech Acts Speech Acts � Consider: � There is some debate about whether this (or � performative = request any!) typology of speech acts is appropriate content = “the door is closed” speech act = “please close the door” � In general, a speech act can be seen to have � performative = inform two components: content = “the door is closed” � a performative verb: speech act = “the door is closed!” (e.g., request, inform, promise, … ) � performative = inquire � propositional content: content = “the door is closed” (e.g., “the door is closed”) speech act = “is the door closed?” 8-9 8-10 Plan Based Semantics Plan-Based Semantics � Here is their semantics for request : � How does one define the semantics of speech request(s, h, φ ) acts? When can one say someone has pre: uttered, e.g., a request or an inform? � s believe h can do φ � Cohen & Perrault (1979) defined semantics of (you don’t ask someone to do something unless you think they can do it) speech acts using the precondition-delete-add � s believe h believe h can do φ list formalism of planning research (you don’t ask someone unless they believe they can do it) � Note that a speaker cannot (generally) force a � s believe s want φ (you don’t ask someone unless you want it!) hearer to accept some desired mental state post: � In other words, there is a separation between � h believe s believe s want φ the illocutionary act and the perlocutionary act (the effect is to make them aware of your desire) 8-11 8-12 2
KQML and KIF KQML and KIF � KQML is an ‘outer’ language, that defines � We now consider agent communication various acceptable ‘communicative verbs’, or languages (ACLs) — standard formats for the performatives exchange of messages Example performatives: � The best known ACL is KQML, developed by � ask-if (‘is it true that. . . ’) the ARPA knowledge sharing initiative � perform (‘please perform the following action. . . ’) KQML is comprised of two parts: � tell (‘it is true that. . . ’) � the knowledge query and manipulation language � reply (‘the answer is . . . ’) (KQML) � KIF is a language for expressing message � the knowledge interchange format (KIF) content 8-13 8-14 KIF – Knowledge Interchange Format KIF – Knowledge Interchange Format � “The temperature of m1 is 83 Celsius”: Used to state: (= (temperature m1) (scalar 83 Celsius)) � Properties of things in a domain (e.g., “Noam � “An object is a bachelor if the object is a man is chairman”) and is not married”: � Relationships between things in a domain (defrelation bachelor (?x) := (e.g., “Amnon is Yael’s boss”) (and (man ?x) (not (married ?x)))) � “Any individual with the property of being a � General properties of a domain (e.g., “All person also has the property of being a students are registered for at least one mammal”: course”) (defrelation person (?x) :=> (mammal ?x)) 8-15 8-16 KQML and KIF FIPA � More recently, the Foundation for Intelligent � In order to be able to communicate, agents must have agreed on a common set of terms Physical Agents (FIPA) started work on a program of agent standards — the � A formal specification of a set of terms is known as an ontology centerpiece is an ACL � The knowledge sharing effort has associated with it a � Basic structure is quite similar to KQML: large effort at defining common ontologies — � performative software tools like ontolingua for this purpose 20 performative in FIPA � Example KQML/KIF dialogue… � housekeeping A to B: (ask-if (> (size chip1) (size chip2))) e.g., sender, etc. B to A: (reply true) B to A: (inform (= (size chip1) 20)) � content B to A: (inform (= (size chip2) 18)) the actual content of the message 8-17 8-18 3
FIPA FIPA � Example: (inform :sender agent1 :receiver agent5 :content (price good200 150) :language sl :ontology hpl-auction ) 8-19 8-20 “Inform” and “Request” “Inform” and “Request” � “Inform” and “Request” are the two basic performatives in FIPA. All others are macro � For the “inform” performative… definitions, defined in terms of these. The content is a statement . Pre-condition is that sender: � The meaning of inform and request is defined in two parts: � holds that the content is true � intends that the recipient believe the content � pre-condition what must be true in order for the speech act to � does not already believe that the recipient is succeed aware of whether content is true or not � “rational effect” what the sender of the message hopes to bring about 8-21 8-22 “Inform” and “Request” � For the “request” performative… The content is an action . Pre-condition is that sender: � intends action content to be performed � believes recipient is capable of performing this action � does not believe that receiver already intends to perform action 8-23 4
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