Agent Communication-Multiagent Systems-Lecture Slides, Slides of Multiagent Systems

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LECTURE 8:

Agent Communication

Agent Communication

• In this lecture and the next, we cover macro-aspects of intelligent agent technology: those issues relating to the agent society , rather than the individual: - communication; speech acts; KQML & KIF; FIPA ACL - cooperation: what is cooperation; prisoner’s dilemma; cooperative versus non-cooperative encounters; the contract net

Speech Acts

• Austin noticed that some utterances are rather like ‘physical actions’ that appear to change the state of the world
• Paradigm examples would be:
  • declaring war
  • christening
  • ‘I now pronounce you man and wife’ :-)
• But more generally, everything we utter is uttered with the intention of satisfying some goal or intention
• A theory of how utterances are used to achieve intentions is a speech act theory

Different Aspects of Speech Acts

• From “A Dictionary of Philosophical Terms and Names”:
• “ Locutionary act: the simple speech act of generating sounds that are linked together by grammatical conventions so as to say something meaningful. Among speakers of English, for example, ‘It is raining’ performs the locutionary act of saying that it is raining, as ‘Grablistrod zetagflx dapu’ would not.”

Different Aspects of Speech Acts

• “ Perlocutionary act: the speech act of having an effect on those who hear a meaningful utterance. By telling a ghost story late at night, for example, one may accomplish the cruel perlocutionary act of frightening a child.”

Speech Acts

• Searle (1969) identified various different types of speech act:
  • representatives: such as informin g, e.g., ‘It is raining’
  • directives: attempts to get the hearer to do something e.g., ‘please make the tea’
  • commisives: 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

Speech Acts

• Consider:
  • 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?”

Plan Based Semantics

• How does one define the semantics of speech acts? When can one say someone has uttered, e.g., a request or an inform?
• Cohen & Perrault (1979) defined semantics of speech acts using the precondition-delete-add list formalism of planning research
• Note that a speaker cannot (generally) force a hearer to accept some desired mental state
• In other words, there is a separation between the illocutionary act and the perlocutionary act

KQML and KIF

• We now consider agent communication languages (ACLs) — standard formats for the exchange of messages
• The best known ACL is KQML, developed by the ARPA knowledge sharing initiative KQML is comprised of two parts: - the knowledge query and manipulation language (KQML) - the knowledge interchange format (KIF)

KQML and KIF

• KQML is an ‘outer’ language, that 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

KIF – Knowledge Interchange Format

• “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))

KQML and KIF

• In order to be able to communicate, agents must have agreed on a common set of terms
• A formal specification of a set of terms is known as an ontology
• The knowledge sharing effort has associated with it a large effort at defining common ontologies — software tools like ontolingua for this purpose
• Example KQML/KIF dialogue… 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))

FIPA

• Example: (inform :sender agent :receiver agent :content (price good

   :language sl :ontology hpl-auction 

  )

FIPA