Agent communication

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Agent communication

• EEL 5937 Multi Agent Systems
• Lecture 10, Feb. 6, 2003
• Lotzi Bölöni

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Speech acts

• Most treatments of communication in multi-agent
  systems borrow their inspiration from speech act
  theory
• Speech act theories are pragmatic theories of
  language they attempt to account for how
  language is used by people every day to achieve
  their goals and intentions.
• The origins of speech act theories are usually
  traced to J.L. Austins book How to do things
  with words.
• This is a phylosophy book with a linguistic
  approach
• Not a computer science book!

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Speech acts (contd)

• 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
• I not 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.

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Speech acts (contd)

• Searle (1969) identified various types of speech
  acts
• Representatives
• Such as informing 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 a war

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Speech acts (contd)

• There is some debate about whether this (or any!)
  typology of speech acts is appropriate
• In general, a speech act can be seen to have two
  components
• A performative verb (e.g. request, inform)
• A propositional content (e.g. the door is
  closed)

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Relationship between the performative and 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?

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Semantics of speech acts

• How can one define the semantics of a speech act?
• What is going to be the affect of the speech act
  to the world?
• More exactly to the receiver?
• The sender agent can not (generally) force a
  receiver agent to accept some desired mental
  state.
• Different formalisms were proposed, depending on
  the representation of the world.

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Plan based semantics

• Cohen Perrault (1979) defined the semantics of
  speech acts using the precondition-delete-add
  list formalism of planning research.
• Semantics for a request request(s, r, a)
• Preconditions
• S believes r can do h
• You dont ask someone to do something unless you
  think they can do it
• S believes h believes h can do a
• You dont ask someone unless they believe they
  can do it
• S believes S wants a
• You dont ask someone unless you want it
• Postconditions
• H believes s believes s wants a
• The effect is to make them aware of your desire.

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Agent communication languages

• We now consider the agent communication languages
  (ACLs), standard formats for the exchange of
  messages.
• KQML
• FIPA-ACL

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KQML

• Developed by the ARPA knowledge sharing
  initiative
• Composed of two parts
• Knowledge Query and Manipulation Language (KQML)
• KQML is an outer language, that defines various
  acceptable communicative acts or performatives
• Many critics say there were too many
  performatives (gt40)
• Knowledge Interchange Format (KIF)
• The content language usually used by KQML

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FIPA ACL, introduction

• FIPA (Foundation for Intelligent Physical Agents)
  non-profit organization
• Companies like IBM, Hitachi, HP, British Telecom,
  Siemens
• Universities and research institutes
• Started work on a program of agent standards, the
  most important being the ACL (1997)

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Basic structure of a FIPA message

• Performative
• There are 20 different performatives in FIPA-ACL
• Housekeeping
• Sender
• Receiver
• Reply-with
• In-reply-to
• Content
• The actual content of the message
• Language
• The language in which the content is written
• Ontology
• The ontology in which the message needs to be
  interpreted.

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Example

• (inform
• sender agent1
• receiver agent2
• content (price milk 100)
• language sl
• ontology hlp-auction
• )

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Performatives in FIPA
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Inform and Request

• Inform and Request are the two basic
  performatives in FIPA ACL.
• All others are macro definitions, defined in
  terms of these.
• The meanings of inform and request are defined in
  two parts
• Pre-condition what must be true in order for the
  speech act to succeed
• Rational effect what the sender hopes that the
  message will bring about.

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Inform

• The content is a statement
• Pre-conditions
• The sender holds that the content is true
• Intends that the recipient believes the content
• Does not already believe that the recipient is
  aware of whether the content is true or not.

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Request

• The content is an action.
• Pre conditions
• The sender intends the action content to be
  performed
• Believes the recipient is capable of performing
  the action
• Does not believe that the sender already intends
  to perform the action.

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FIPA ACL, Semantic Language, SL

• Used to define the semantics of FIPA ACL
• Quantified, multi-modal logic with operators for
  beliefs, desires, uncertain beliefs and
  intentions
• Can represent propositions, objects and actions