Design of Multi-Agent Systems

Design of Multi-Agent Systems • Teacher • Bart Verheij • Student assistants • Albert Hankel • Elske van der Vaart • Web site • http://www.ai.rug.nl/~verheij/teaching/dmas/ • (Nestor contains a link)

Overview • Speech acts • Agent communication languages • Interaction protocols • Ontologies

Speech Acts • Speech act theories are pragmatic theories of language, i.e., theories of language use • Speech act theories go beyond syntax and semantics • Pragmatics: language is used by people every day to achieve their goals and intentions • Example: • Can you pass me the cheese, please?

Speech Acts • Origin of speech act theories: • Austin’s 1962 book, How to Do Things with Words • Austin noticed that some utterances are rather like ‘physical actions’ that appear to change the state of the world • Declaring war • ‘I now pronounce you man and wife’ • Deciding a legal case (by a judge)

Speech Acts Wikipedia: A locutionary act is the act of saying something, the locution. An illocutionary act is any speech act that amounts to stating, questioning, commanding, promising, and so on. It is an act performed in saying something A perlocutionary act is any speech act that amounts to persuading, convincing, scaring, enlightening, inspiring, or otherwise getting someone to do or realize something. When examining perlocutionary acts, the effect in the hearer or reader is emphasized.

Speech Acts • Somewhere else on the Internet: • Locution--the semantic or literal significance of the utterance; • Illocution--the intention of the speaker; and • Perlocution--how it was received by the listener.

Speech Acts • Some functions of communication: • Changing someone’s beliefs • Getting someone to do something for you • Promising something to someone • Changing the world

Speech Acts • Types of speech act (Searle 1969): • 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

Speech Acts • Components of speech acts: • a performative verb:(e.g., request, inform, promise, … ) • propositional content:(e.g., “the door is closed”)

Speech Acts • “Please close the door performative = request content = “the door is closed” • “The door is closed!” performative = inform content = “the door is closed” • “Is the door closed?” performative = inquire content = “the door is 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 preconditions and postconditions • 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

Plan-Based Semantics • request(s, h, f) • pre: • s believe h can do f(you don’t ask someone to do something unless you think they can do it) • s believe h believe h can do f(you don’t ask someone unless they believe they can do it) • s believe s want f(you don’t ask someone unless you want it!) • post: • h believe s believe s want f(the effect is to make them aware of your desire)

Agent communication languages • KQML (Knowledge Query and Manipulation Language) DARPA • ACL (Agent Communication Language) Foundation for Intelligent Physical Agents (FIPA)

Agent Communcation Language (ACL) • The structure of an ACL message • KQML is similar. • In KQML, a communicative act is called a performative.

FIPA performatives

Communicative Act • Meaning of inform according to FIPA: • Feasibility preconditions (FE): Bi  Bi( (Bj  Bj)  (Uj  Uj) ) • Rational effect (RE): Bj Bj: agent j believes that . Uj: agent j is uncertain about , but considers it more likely than . See the FIPA Communicative Act Library Specification op www.fipa.org

Communicative Act • Meaning of request according to FIPA: • Feasibility preconditions (FE): FP(a)[i/j]  Bi Agent(j,a)  Bi Ij Done(a) • Rational effect (RE): Done(a) FP(a)[i/j]: the part of the FPs of action a which are mental attitudes of i Agent(j,a): j is the only agent that ever performs action a. Ij: agent j has the intention . Done(a): action a is done.

Communicative Act • (request • :sender (agent-identifier :name i) • :receiver (set (agent-identifier :name j)) • :content • "open \"db.txt\" for input" • :language vb)

Languages for message content • Knowledge Interchange Format (KIF) First order logic in LISP notation • Semantic Language (SL) (FIPA standard) A modal logic with beliefs, desires, intentions en uncertain beliefs

Protocols • An ACL message can mention a protocol. A protocol specifies the messages that can be exchanged • FIPA has provided a number of standard Interaction Protocols (IPs). There can be exceptions to the normal flow of an Interaction Protocol (e.g., in case a message is not understood).

Ontologies • An ACL message can specify an ontology • An ontology specifies the meaning of the concepts in a language. It is a specification of a domain conceptualization. • An ontology specifies concepts and their relations • E.g., Dublin Core: a specification of meta-tags for web pages • Title, Creator, Subject, Description, Publisher, Contributor, Date, Type, Format, Identifier, Source, Language, Relation, Rights

Ontologies country European oak is_a grows_in oak is_a is_a American oak tree is_a chestnut has_a has_a has_a trunk branch leaf has_a has_a has_a is_a shape structure color green

Ontologies • The Semantic Web movement aims at making the web’s content more accessible to machines • Specify message content in XML or RDF • Specify message grammar in XML Schema or RDFS • Specify the ontology in RDFS or OWL • Standards: www.w3c.org • Tool: protege.stanford.edu

Student presentations

Design of Multi-Agent Systems