Agent communication EEL 5937 Multi Agent Systems Lecture
- Slides: 18
Agent communication EEL 5937 Multi Agent Systems Lecture 10, Feb. 6, 2003 Lotzi Bölöni EEL 5937
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. Austin’s book “How to do things with words”. – This is a phylosophy book with a linguistic approach – Not a computer science book! EEL 5937
Speech acts (cont’d) • 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. EEL 5937
Speech acts (cont’d) • 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 EEL 5937
Speech acts (cont’d) • 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”) EEL 5937
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? ” EEL 5937
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. EEL 5937
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 don’t ask someone to do something unless you think they can do it – S believes h can do a » You don’t ask someone unless they believe they can do it – S believes S wants a » You don’t ask someone unless you want it • Postconditions: – H believes s wants a » The effect is to make them aware of your desire. EEL 5937
Agent communication languages • We now consider the agent communication languages (ACL’s), standard formats for the exchange of messages. • KQML • FIPA-ACL EEL 5937
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 (>40) • Knowledge Interchange Format (KIF) – The content language usually used by KQML EEL 5937
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) EEL 5937
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. EEL 5937
Example (inform : sender agent 1 : receiver agent 2 : content (price milk 100) : language sl : ontology hlp-auction ) EEL 5937
Performatives in FIPA EEL 5937
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. EEL 5937
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. EEL 5937
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. EEL 5937
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 EEL 5937
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