Presentation on theme: "Peer-to-peer and agent-based computing Agent communication."— Presentation transcript:
peer-to-peer and agent-based computing Agent communication
peer-to-peer and agent-based computing 2 Plan for next two lectures Communication Agent Communication Languages Communication Protocols
peer-to-peer and agent-based computing 3 Agent Communication For agents to communicate they must agree on: –The syntax of individual messages (i.e., the language) –The sequence of messages (i.e., the protocol) – N.B.1: Languages are distinct from protocols! – N.B.2: We need both! We shall look at proposals for –Agent communication languages (ACLs) –Description of protocols
peer-to-peer and agent-based computing 4 Agent Communication (Contd) Agents are different from distributed processes, as far as their message exchanges: –Individual messages may contain sophisticated information or knowledge E.g., a message with an explanation of a diagnosis –Protocols are more complex E.g., a many-party argumentation over fishing rights
peer-to-peer and agent-based computing 5 How to do Things With Words J.L. Austin –How To Do Things with Words (1962) http://en.wikipedia.org/wiki/J._L._Austin – Speech acts can change the state of the world – E.g., I pronounce you man and wife Locutionary act –Act of making an utterance –E.g., Shut the door!. Illocutionary act –Action performed in saying something –E.g., He told me to shut the door. Perlocution –The effect of the act –E.g., He caused me to shut the door.
peer-to-peer and agent-based computing 6 Background: Speech Acts John Searle (1969), Speech Acts –Home page: http://socrates.berkeley.edu/~jsearle/ –Extended Austins theory: Properties required for a speech act to succeed –Wikipedias entry: http://en.wikipedia.org/wiki/Speech_Act For an imperative: –Normal I/O conditions state that the hearer is able to hear the request, the act was performed in normal circumstances. –Preparatory conditions state what must be true for this speech act to be effective, e.g., the hearer must be capable of the action requested, and the speaker must believe the hearer can do it. –Sincerity conditions state, for example, that the speaker really does want the action performed.
peer-to-peer and agent-based computing 7 Searle: Types of Speech Acts Representatives: –Commits speaker to the truth of an expressed proposition Directives: –Attempt to get the hearer to do something (an imperative) Commissives: –Commits the speaker to some course of action Expressive: –Express some psychological state Declaratives: –Causes a change in an institutional state of affairs
peer-to-peer and agent-based computing 8 Agent Communication Languages Agents exchange messages expressed in an Agent Communication Language (ACL) –Parties must agree (or be aware) of the syntax of individual messages Most ACLs identify distinct kinds of messages –They represent the intention of the speaker Examples: –Indicatives (representatives) – The cat is on the mat. –Imperatives (directives) – Put the cat on the mat! –Interrogatives – Where is the cat?
peer-to-peer and agent-based computing 9 Message Structure Based on communicative acts (CAs), i.e., the performatives: –Illocutionary verbs, i.e., they describe the speakers intention –ACL = CA + MSG ACLs provide a mechanism for context: –sender, receiver, ontology, protocol, etc. Message expressed in some Agent Communication Language Sender: Agent-name Receiver: Agent-name Message content expressed in a content language, refers to an ontology
peer-to-peer and agent-based computing 10 KQML Knowledge Query Manipulation Language –Wikipedias entry: http://en.wikipedia.org/wiki/Knowledge_Query_and_Manipulation_Lan guage Developed in the early 1990s Originally conceived as an interface to KBSs –Repurposed as an ACL… Web site: http://www.cs.umbc.edu/kqml/
peer-to-peer and agent-based computing 11 KQML ACL KQML messages are of the form For example: (performative :sender S :receiver R :language L :ontology O :in-reply-to I1 :reply-with I2 :content K ) (ask-one :sender shopper :receiver amazon-agent :language prolog :ontology book-ontology :in-reply-to advert1234 :reply-with q321 :content book(How to do things with words,Austin,Price) )
peer-to-peer and agent-based computing 12 KQML (Informal) Semantics In 1997 KQML had 35 performatives, including: ask-if S wants to know if K is in Rs KB ask-all S wants to know all instantiations of K that are true ask-one S wants one instantiation of K that is true in Rs KB tell K is in Ss KB insert S asks R to add K to its KB advertise S wants R to know that S can process K broker-one S wants R to provide one response to K (some agent other than R is going to provide the response) broker-all S wants R to provide all responses to K (some agents other than R are going to provide the responses) recommend-one S wants to learn of an agent who can respond to K recommend-all S wants to learn of all agents who can respond to K
peer-to-peer and agent-based computing 14 Recommend-Style Facilitation Conversation for recommend-style facilitation: 1.Agent A advertises to broker B that it can supply K 2.Originator O requests recommendation from B for a supplier of K 3.B sends O advertisement that A can supply K 4.O asks A a query Q concerning K. 5.A tells O some information I in response to Q. Advantage: O can cache advert message for later reuse OA B 1. advertise K 3. advertise K 2. recommend K? 4. ask Q 5. tell I
peer-to-peer and agent-based computing 15 Broker-Style Facilitation Alternative style of brokerage: middleperson 1.A advertises to B that it can supply K, as before. 2.O requests B to act as broker for a query Q. 3.B determines that Q concerns K, so asks Q to A. 4.A tells B a response I to Q. 5.B tells I to O. Advantage: agent O only needs to know the broker OA B 1. advertise K 5. tell I 2. broker Q 3. ask Q 4. tell I
peer-to-peer and agent-based computing 16 FIPA ACL The Foundation for Intelligent Physical Agents –Standards organisation promoting agent-based technology –Goal: interoperability of standards with other technologies –Web site: http://www.fipa.orghttp://www.fipa.org The FIPA ACL –Open standard described at http://www.fipa.org/specs/fipa00061/SC00061G.pdf –Based on ARCOL (Sadek) & KQML Content –content languages FIPA SL, constraint language, KIF, RDF. FIPA interaction protocols –Conversations to achieve some interaction or effect; e.g. auction, contract net, negotiation.
peer-to-peer and agent-based computing 17 FIPA: Message Structure FIPA-ACL messages consist of the following parameters: ParameterDescription performativetype of communicative act senderidentity of agent sending the message receiveridentity of intended recipient of message reply-to id of agent to which subsequent messages should be directed contentobject of the communicative action languagesyntax of the content of the message
peer-to-peer and agent-based computing 18 FIPA: Message Structure (Contd) ParameterDescription encodingspecific encoding of content expression ontologysemantics (meaning) of content protocolinteraction protocol of which message is part conversation-idunique identifier of the conversation reply-with identifier (local to this conversation) for the response to this message in-reply-toidentifier of the message this is a response to reply-bydeadline for the reply
peer-to-peer and agent-based computing 19 Message Structure (Contd) Only mandatory element is performative –However, most messages will also have at least the sender, receiver and content If an agent is unable to process one or more element of a message, it must respond with not- understood –An agent that complies with FIPA ACL must at least support not-understood
peer-to-peer and agent-based computing 20 (request :sender (:name firstname.lastname@example.org:8080) :receiver (:name rexhotel@tcp://hotelrex.com:6600) :ontology personaltravelassistant :language FIPA-SL :protocol fipa-request :content (action movenpickhotel@tcp://movenpick.com:6600 (bookhotel (:arrival 25/11/2000) (:departure 05/12/2000)...)) ) Sample Message A request for a hotel booking:
peer-to-peer and agent-based computing 21 Another example: Inform Summary: –Sender informs receiver that something is true Message Content: a fact Description – the sending agent: 1.Believes that some fact is true, 2.Intends that the receiving agent also comes to believe that the fact is true, and, 3.Does not already believe that receiver has any knowledge of the truth of the fact.
peer-to-peer and agent-based computing 22 Sending agent is sincere –Has (somehow) generated the intention that the receiver should know the fact. Last property concerns semantic soundness of the act: –If an agent knows already that some state of the world holds (that the receiver knows fact p), THEN –It cannot rationally adopt an intention to bring about that state of the world –A rational agent X should never adopt an intention to tell Y something that X knows that Y already knows… Another example: Inform (Contd)
peer-to-peer and agent-based computing 23 Another example: Inform (Contd) From the receiver's viewpoint, receiving an inform message entitles it to believe that: –The sender believes the fact contained in the message, and, –The sender wishes the receiver to believe that fact also Whether or not receiver adopts the belief in the fact will be determined by the receivers trust in the sincerity and reliability of the sender
peer-to-peer and agent-based computing 24 Other Performatives FIPA Communicative Act Library Specification Includes: –request an agent to perform some action –query (ask a question) –propose a deal during negotiation –accept-proposal to commit to an agreement –reject-proposal to terminate negotiation without agreement –etc.
peer-to-peer and agent-based computing 25 FIPA ACL and JADE JADE: FIPA-compliant platform Incorporates FIPA ACL –Functionalities to assemble and parse messages in FIPA- ACL –Pushing a standard onto industry