1 / 36

Software Agent -communication-

Software Agent -communication-. Outline. Overview Speech act theory Agent communication languages Summary. Example: Personal Assistant Agent (PA). Task: organize an evening with Heikki What is needed? Participants’ calendar info Info about restaurants, pubs, etc.

Download Presentation

Software Agent -communication-

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.


Presentation Transcript

  1. Software Agent-communication-

  2. Outline Overview Speech act theory Agent communication languages Summary

  3. Example: Personal Assistant Agent (PA) • Task: organize an evening with Heikki • What is needed? • Participants’ calendar info • Info about restaurants, pubs, etc. • Weather forecast Multi-agent System

  4. Example: Organizing Evening (1) DA Calendar Who takes care of Heikki’s Calendar? PAA HCA It is HCA and address is http:…; MTP is…; Presentation is …; CL is…; Ontology is …; … Give me Heikki’s free evenings in this week? Heikki is free on Tuesday and Friday evening

  5. Example: Organizing Evening (2) Calendar I want to book Friday evening PAA HCA No, I don’t want to book Friday evening I want to book Tuesday evening Tuesday evening booked

  6. Example: Sending a Message to an Agent Allocate time from Heikki’s calendar Find out Heikki’s calendar agent Who takes care of Heikki’s Calendar? To: DF@HAP Query Heikki Calendar Service

  7. Layered Model

  8. Agent Communication Language • Definition • An agent communication language (ACL) allows agents to communicate with each other about their positions and actions • An agents communication language (ACL) provides agents with a means of exchanging information and knowledge • Earlier attempts at seamless exchange of information and knowledge between applications • e.g. Remote Procedure Calls, Remote Method Invocation, CORBA • Differences between the above and ACLs are • Semantic complexity • ACLs can handle propositions, rules and actions instead of simple objects with no semantics associated with them • An ACL message describes a desired state in a declarative language, rather than a procedure or a method

  9. Agent Communication • Agents have conversations (as opposed to exchange single messages), e.g. • Task-oriented • Negotiations • A higher level conceptualization of an agent’s strategies drive an agent’s communicative behavior • Message type of agents : Speech acts

  10. Speech Acts (1) • Communication in MAS is inspired by 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 origin of speech act theories are usually traced to the work of the philosopher John Austin • Austin noticed that some utterances are like ”physical actions” that appear to change the state of the world. e.g. • Declaring war • ”I now pronounce you man and wife” • In general, every thing 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

  11. Speech Acts (2) • Austin distinguished 3 different aspects of speech acts: • Locutionary act - act of making an utterance • e.g. saying ”please make some tea” ’ • Illocutionary act – action performed in saying something • e.g. he requested me to make some tea • Perlocution – effect of the act • e.g. he got me to make tea • Searle identified 5 different types of speech acts:

  12. Speech Acts (3) • In general, speech acts can be seen to have 2 components: • A performative verb • e.g. Request, inform • Propositional content • e.g. ”the window is closed”

  13. Speech Acts (4) • How does one define the semantics of speech acts? When can one say someone has uttered, e.g. a request or an inform? • How can the properties of speech acts be represented such that planning systems could reason about them? • Speech acts are treated as physical actions • Actions are characterised via preconditions and postconditions • Semantics for request: request(s,h,) • Pre: • s believes h can do (you don’t ask someone to do something unless you think that they can do it) • s believes h believes h can do  (you don’t ask someone unless they believe they can do it) • s believes s wants  (you don’t ask someone unless you want it!) • Post: • h believes s believes s wants  (the effect is to make them aware of your desire)

  14. Goal G Agenti Agentj Intent I Perform-ative Message Convert to transport form Convert to transport form Message delivery/transportation service Agent Communication Language (ACL) (Meaning is a combination of semantics and pragmatics) • ACLs allow agents to effectively communicate and exchange knowledge with other agents • Three important aspects • Syntax: How the symbols of communication are structured • Semantics: What the symbols denote • Pragmatics: How the symbols are interpreted

  15. Communication Levels Semantics Meaning of the information Syntax Format of information being transferred Communication Method of interconnection • Requirements for an ACL • Syntactic translation between languages • Semantic content preservation among applications • The concept must have a uniform meaning across applications. • Ability to communicate complex attitudes about their information and knowledge. • Agents need to question, request, etc. • Not about transporting bits and bytes.

  16. Origins of ACLs • Knowledge Sharing Effort (KSE), funded by ARPA • Central concept: knowledge sharing requires communication, which in turn requires a common language. KSE focused on defining that common language • KQML: Knowledge Query and Manipulation Language • Language for both message formatting and message handling protocols • KIF: Knowledge Interchange Format • Language for expressing message content

  17. KIF • Creation of a common language for expressing properties • Intended to express contents of a message; not the message itself • Based on first-order logic • Using KIF, it’s possible to express: • Properties of things in a domain (e.g. Michael is a vegetarian) • Relationships between things in a domain (e.g. Michael and Janine are married) • General properties of a domain (e.g. Everybody has a mother) • Example • Relation between 2 objects: • The temperature of m1 is 83 Celsius: • (= (temperature m1) (scalar 83 Celsius)) • Definition of new concept: • An object is a bachelor if this object is a man and not married: • (defrelation bachelor (?x) := (and (man ?x) (not (married ?x)))) • Relationship between individuals in the domain: • A person with the property of being a person also has the property of being a mammal: • (defrelation (person ?x) :=> (mammal ?X))

  18. Communication Mechanics of communication, e.g. Sender, receiver. Performatives (message layer) Logic of communication, e.g. ask, tell. Content Content of communication, e.g. a KIF expression KQML: Overview e.g. (ask-if :sender agenti :receiver agentj :language Prolog :ontology genealogy :content “spouse(adam, eve)”) • An “outer language” that defines a set of performatives (communicative acts), such as ask, reply • Performatives form the core of the language: • Determine the kinds of interactions one can have with KQML-speaking agents • Identify the protocol to be used to deliver the message • Signify that the content is an assertion, a query, a command or another speech act • Describe how the sender would like any reply to be delivered

  19. KQML: Categories of Performatives

  20. KQML: Example (evaluate :sender A : receiver B :language KIF: ontology motors :reply-with q1 :content (val (torque m1))) (reply :sender B : receiver A :language KIF: ontology motors :in-reply-to q1 :content (= (torque m1) (scalar 12 kgf))) (stream-about :sender A : receiver B :language KIF: ontology motors :reply-with q1 :content (m1) (tell :sender B : receiver A :in-reply-to q1 :content (= (torque m1) (scalar 12 kgf))) (tell :sender B : receiver A :in-reply-to q1 :content (= (status m1) (normal))) (eos :sender B : receiver A :in-reply-to q1)

  21. Facilitators • KQML environments (may) contain facilitators that help make the communication protocol transparent • Facilitators: a special class of agents that perform useful communication services such as: • Maintain registry of service names • Forward messages to named services • Routing messages based on content • Provide matchmaking between information providers and seekers • Provide mediation and translation services

  22. F tell(X) ask(X) A B Facilitators: Example (1) Point-to-point protocol A is aware that it is appropriate to send a query about X toB There are several ways to achieve this via a Facilitator.

  23. Facilitators: Example (2) Using the subscribe performative Request that Facilitator F monitor for the truth of X. If B subsequently informs F that it believes X to be true, then F can in turn inform A tell(X) subscribe(ask(X)) F tell(X) A B

  24. advertise(ask(X)) broker(ask(X)) tell(X ) F tell(X ask(X) ) A B Facilitators: Example (3) Using the broker performative A Asks Facilitator to find another agent which can process a given performative

  25. advertise(ask(X)) recruit(tell(X)) F ask(X) tell(X ) A B Facilitators: Example (4) Using the rercruit performative Asks Facilitator to find an appropriate agent to which an embedded performative can be forwarded. A reply is returned directly to the original agent

  26. recommend(ask(X)) advertise(ask(X)) reply(B) F ask(X) A B tell(X) Facilitators: Example (5) Using the recommend performative Asks Facilitator to respond with the ”name” of another agent which is appropriate for sending a particular performative.

  27. Discussion on KQML • Weak semantics of performatives • Different implementations of KQML could not interoperate • Transportation mechanisms were not defined • Lacked the class of performatives: commissives • Difficult to implement multi-agent scenarios without commissives • Set of performatives was large and ad hoc • Recently, more efforts have been made to provide formal semantics in terms of preconditions, postconditions and completion conditions (ref: Labrou et. al., 1999.)

  28. FIPA The Foundation for Intelligent Physical Agents (FIPA) is a non-profit association FIPA’s purpose is to promote the success of emerging agent-based applications, services and equipment FIPA operates through the open international collaboration of member organizations: companies, universities and government organizations

  29. FIPA ACL (1) Envelope (transport information) Message body (ACL message) (inform :sender agentA :receiver agentB :content (price good200 150) :language sl :ontology hpl-auction ) • Basic structure is quite similar to KQML: • Performative (communicative act) • 20 performatives in FIPA ACL • Housekeeping • e.g. Sender • Content • the actual content of the message • Message structure (Envelope): • Comprises of a collection of parameters • Contains at least the mandatory to and sender parameters • Example FIPA ACL message

  30. FIPA ACL (2) • 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 meaning of inform and request are defined in 2 parts: • Precondition: What must be true in order for the speech act to succeed • Rational effect: What the sender of the message hopes to bring about

  31. Agent Platform Agent A Agent Platform Agent B Agent Communication Channel Agent Communication Channel FIPA Message Transport Model ACL message sent over the Message Transport Service Message Transport Protocol

  32. Agent Platform Agent A Agent Platform Agent B 3 2 1 1&2 1 Agent Communication Channel Agent Communication Channel FIPA Sending Messages • 3 options • Via local ACC • Via remote ACC • Direct communication mechanism

  33. cfp action preconditions1 Not-understood refuse reason propose preconditions2 Deadline for proposals Manager cancels the contract due to a change reject-proposal reason accept-proposal proposal failure reason inform Done(action) cancel reason FIPA Agent Interaction Protocol (1) manager Potential contractors • Ongoing conversations between agents fall into typical patterns. In such cases, certain message sequences are expected, and at any point in the conversation, other messages are expected to follow. • These typical patterns of message exchange are called protocols (request :sender A :receiver B :content some-act :protocol fipa-contract-net )

  34. FIPA Agent Interaction Protocol (2) Manager Potential contractors cfp refuse deadline not-understood propose reject-proposal accept-proposal cancel inform

  35. Comparison between KQML & FIPA ACL • Similarities: • Separation of the outer language (performative) and the inner language (content). • Allows for any content language • Differences • Communication primitives: • KQML – performative • FIPA ACL – communicative act • Different semantic frameworks – impossible to come up with an exact mapping or transformation between KQML and FIPA performatives • KQML provides facilitator services; FIPA ACL does not

  36. Summary • Agent communication • Speech act theory • Agent communication languages • Open issues • How do we verify whether an agent complies with the semantic definition? • E.g. If an agent sends a message ( say inform Ф), how do we know whether the agent believe Ф or not • Is sincerity a tall-order for agent society? • E.g negotiation • Can we specify semantics without a context? • E.g. Query If in an oral examination setting • We need a context (protocol) • Next lecture: Application & review

More Related