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CPE/CSC 580: Intelligent Agents Franz J. Kurfess Computer Science Department California Polytechnic State University San Luis Obispo, CA, U.S.A. 1 Course Overview ❖ ❖ Introduction Intelligent Agent, Multi-Agent Systems Agent Examples Agent Architectures ❖ Reasoning Agents ❖ Agent Encounters, Resource Sharing, Agreements Communication ❖ Observation, Analysis, Performance Improvement Multi-Agent Interactions ❖ Knowledge, Reasoning, Planning Learning Agents ❖ Agent Hierarchy, Agent Design Principles Speech Acts, Agent Communication Languages Collaboration © Franz J. Kurfess 3 Overview Communication among Agents ❖ Motivation ❖ Objectives ❖ Communication ❖ speech acts; agent communication languages Cooperation self-interest, societal benefits ❖ Important Concepts and Terms ❖ Chapter Summary © Franz J. Kurfess 4 Motivation © Franz J. Kurfess 7 Objectives © Franz J. Kurfess 8 Communication Communication Basics Speech Acts Language: Syntax, Semantics, Pragmatics 10 Basic Concepts ❖ communication exchange of information requires a shared system of signs greatly enhanced by language speaker produces signs as utterances general: not only spoken language listener (hearer) perceives and interprets signs © Franz J. Kurfess 11 Communication among Agents [Woolridge 2009] 12 Purpose of Communication ❖ sharing of information among agents or systems query other agents for information responses to queries requests or commands offer proposition for collaboration acknowledgement actions to be performed for another agent confirmation of requests, offers sharing of experiences, feelings © Franz J. Kurfess 13 Communication Problems ❖ intention ❖ timing ❖ what sign system should be used interpretation ❖ which act is the right one language ❖ when is a communication act appropriate selection ❖ what is the expected outcome (speaker’s perspective) will the intended meaning be conveyed to the listener ambiguity can the intention be expressed without the possibility of misunderstandings © Franz J. Kurfess 14 Language and Communication ❖ Natural Language ❖ used by humans evolves over time moderately to highly ambiguous Formal Languages invented rigidly defined little ambiguity © Franz J. Kurfess 15 Natural Language ❖ formal description is very difficult ❖ mostly used for human communication ❖ sometimes non-systematic, inconsistent, ambiguous easy on humans tough on computers context is critical situation, beliefs, goals © Franz J. Kurfess 16 Formal Languages ❖ symbols terminal symbols finite set of basic words not: alphabet, characters non-terminal symbols ❖ strings ❖ intermediate structures composed of terminal or non-terminal symbols sequences of symbols phrases sub-strings grouping important parts of a string © Franz J. Kurfess 17 Formal Languages Cont. ❖ sentences ❖ grammar ❖ allowable strings in a language composed from phrases rules describing correct sentences often captured as rewrite rules in BNF notation lexicon list of allowable vocabulary words © Franz J. Kurfess 18 Communication Models ❖ encoded message model ❖ a definite proposition of the speaker is encoded into signs which are transmitted to the listener the listener tries to decode the signs to retrieve the original proposition errors are consequences of transmission problems situated language model the intended meaning of a message depends on the signals as well as the situation in which they are exchanged mis-interpretation may lead to additional problems © Franz J. Kurfess 19 Communication Types ❖ telepathic communication ❖ speaker and listener have a shared internal representation communication through Tell/Ask directives language-based communication speaker performs actions that produce signs which other agents can perceive and interpret communication language is different from the internal representation more complex involves several mappings language needs to be generated, encoded, transmitted, decoded, and interpreted © Franz J. Kurfess 20 Telepathic Communication © Franz J. & Kurfess [Russell Norvig 1995] 21 Language-Based Communication © Franz J. & Kurfess [Russell Norvig 1995] 22 Communication Steps: Speaker ❖ intention ❖ generation ❖ decision about producing a speech act conversion of the information to be transferred into the chosen language synthesis actions that produce the generated signs © Franz J. Kurfess 23 Communication Steps: Listener ❖ perception reception of the signs produced by the speaker analysis syntactic interpretation (parsing) semantic interpretation disambiguation speech recognition, lip reading, character recognition selection of the most probable intended meaning incorporation the selected interpretation is added to the existing world model as additional piece of evidence © Franz J. Kurfess 24 Communication Example © Franz J. Kurfess [Russell & Norvig 1995] 25 Speech Acts Basics Speech Act Theory Mappings Components Semantics 26 Speech Act ❖ used for the production of language ❖ independent of the communication mode ❖ word ❖ basic meaningful communicative sign smaller entities may exist e.g. syllable, phonem, letter don’t carry meaning speaker (sender) ❖ talking, sign language, typing, flags producer of an utterance hearer (listener, recipient) consumer of an utterance © Franz J. Kurfess 27 Speech Act Theory ❖ developed in linguistics, cognitive science, communication theory ❖ pragmatic theories of language ❖ utterances ❖ based on language use elementary speech actions based on or related to intentions different typologies of speech acts © Franz J. Kurfess 28 Speech Acts - Searle Searle (1969) identified various different types of speech act: representatives: such as informing, e.g., ‘It is raining’ directives: attempts to get the hearer to do something e.g., ‘please make the tea’ commissives: 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 [Woolridge 2009] 8-8 29 Speech Act Components a performative verb: e.g., request, inform, promise, … propositional content: e.g., “the door is closed” [Woolridge 2009] 8-9 30 Speech Act Mappings Speech act <=> performatives & content: performative = request content = “the door is closed” speech act = “please close the door” performative = inform content = “the door is closed” speech act = “the door is closed!” performative = inquire content = “the door is closed” speech act = “is the door closed?” [Woolridge 2009] 8-10 31 Speech Act Semantics intention of the speaker interpretation by the listener leads to a specific formulation of a statement may be different from the intended meaning methods from other AI areas have been applied e.g. planning [Woolridge 2009] 32 Agent Communication Languages standard formats for the exchange of knowledge and information usually based on messages 33 KQML KQML (Knowledge Query and Manipulation Language) developed by the ARPA knowledge sharing initiative KIF (Knowledge Interchange Format) designed to work in conjunction with KQML [Woolridge 2009] 34 KQML and KIF KQML is an ‘outer’ language defines various acceptable ‘communicative verbs’, or performatives Example performatives: ask-if (‘is it true that. . . ’) perform (‘please perform the following action. . . ’) tell (‘it is true that. . . ’) reply (‘the answer is . . . ’) KIF is a language for expressing message content related to knowledge representation languages [Woolridge 2009] 35 KIF – Knowledge Interchange Format Used to state: Properties of things in a domain Relationships between things in a domain e.g., “Orna is chairman” e.g., “Michael is Yael’s boss” General properties of a domain e.g., “All students are registered for at least one course” [Woolridge 2009] 36 KIF Examples “The temperature of m1 is 83 Celsius”: (= (temperature m1) (scalar 83 Celsius)) “An object is a bachelor if the object is a man and is not married”: (defrelation bachelor (?x) := (and (man ?x) (not (married ?x)))) “Any individual with the property of being a person also has the property of being a mammal”: (defrelation person (?x) :=> (mammal ?x)) [Woolridge 2009] 37 KQML and KIF communication between agents requires a common set of terms ontology formal specification of a set of terms knowledge sharing requires defining common ontologies OWL - Web Ontology Language ontology editors Protégé [Woolridge 2009] 38 KQML/KIF Dialogue Example A to B: (ask-if (> (size chip1) (size chip2))) B to A: (reply true) B to A: (inform (= (size chip1) 20)) B to A: (inform (= (size chip2) 18)) [Woolridge 2009] 39 Criticisms of KQML fluid performative set transport mechanisms not precisely defined semantics not rigorously defined missing commissives leading to interoperability problems performatives for making commitments performative set too large and ad hoc [Woolridge 2009] 40 FIPA Agent Communication Language program of agent standards initiated by the Foundation for Intelligent Physical Agents (FIPA) the centerpiece is an ACL structure similar to KQML performatives 20 performatives in FIPA content the actual content of the message housekeeping e.g., sender, receiver, ... [Woolridge 2009] 41 FIPA ACL Example Example: (inform :sender :receiver :content :language :ontology ) agent1 agent5 (price good200 150) sl hpl-auction [Woolridge 2009] 42 FIPA Performatives [Woolridge 2009] 43 “Inform” and “Request” two basic performatives in FIPA all others are macro definitions defined in terms of “Inform” and “Request”. semantics of “Inform” and “Request” pre-condition what must be true in order for the speech act to succeed “rational effect” what the sender of the message hopes to bring about [Woolridge 2009] 44 “Inform” pre-condition is that the sender holds that the content is true intends that the recipient believe the content does not already believe that the recipient is aware of whether content is true or not content is a statement [Woolridge 2009] 45 “Request” pre-condition is that the 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 content is an action [Woolridge 2009] 8-24 46 Summary Communication © Franz J. Kurfess 49 Important Concepts and Terms ❖ agent ❖ Agent Communication Language ❖ alphabet ❖ ambiguity ❖ communication ❖ collaboration ❖ coordination ❖ formal language ❖ grammar ❖ hearer ❖ KIF ❖ KQML ❖ language ❖ lexicon © Franz J. Kurfess 50