multi-agent systems chapter 2 adapted (with permission) from adina magda florea adina@wpi.edu

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  • Slide 1
  • Multi-Agent Systems Chapter 2 Adapted (with permission) from Adina Magda Florea adina@wpi.edu
  • Slide 2
  • 2 Candy Quiz (not for points, just for candy) What do each of the following mean? KQML ACL Ontology Illocution KSE FIPA KIF
  • Slide 3
  • 3 Candy Quiz (not for points, just for candy) What do each of the following mean? KQML Knowledge Query Manipulation Language ACL Agent Communication Language Ontology specification of objects, concepts and relationship Illocution intended meaning - performative KSE Knowledge Sharing Efort FIPA Foundation for Intelligent Physical Agents KIF Knowledge Interchange Format
  • Slide 4
  • 1. The nature of communication Human communication Communication is the intentional exchange of information brought about by the production and perception of signs drawn from a shared system of conventional signs (AIMA, Russell&Norvig) language Communication seen as an action (communicative act) and as an intentional stance (want something to happen) Component steps of communication SpeakerHearer Intention Perception Generation- create Analysis Synthesis- organize Disambiguation Incorporation 4 Syntax-how structured Semantics-symbol meaning Pragmatics-interpretation
  • Slide 5
  • Artificial Communication low-level language vs high-level languages direct communication vs. indirect communication Computer communication shared memory message passing Agent communication/ MAS communication Communication in MAS = more than simple communication, implies interaction The environment provides a computational infrastructure where interactions among agents take place. The infrastructure includes protocols for agents to communicate and protocols for agents to interact 5
  • Slide 6
  • Communication protocols = enables agents to exchange and understand messages Interaction protocols = enable agents to have conversations, i.e., structured exchanges of messages. Can trace series of responses. Aim Communication enables agents to: coordinate their actions and behavior attempt to change state of the other agents attempt to get other agents perform actions 6
  • Slide 7
  • kCommunication infrastructure kblackboard (shared memory) or message-based kconnected or connection-less (email) k point-to-point (1), multicast (some), broadcast (all) kpush or pull (information given to you or requested) ksynchronous or asynchronous
  • Slide 8
  • 8 Dimensions of Meaning (think of examples of each) Descriptive/Prescriptive: describe phenomenon vs proscribe behavior (I am cold) Personal/conventional: different meaning to individual Semantics/Pragmatics: interpreted differently than intended: mental states Contextuality: cannot be understood in isolation Coverage: language express necessary concepts Identity: meaning is dependent on individual Cardinality: private message interpreted differently than public message
  • Slide 9
  • 2. Indirect communication 2.1 Signal propagation - Manta, A. Drogoul 1993 An agent sends a signal, which is broadcast into the environment, and whose intensity decreases as the distance increases At a point x, the signal may have one of the following intensities (why?) V(x)=V(x 0 )/dist(x,x 0 ) V(x)=V(x 0 )/dist(x,x 0 ) 2 9 x0x0 Agent A (stimulus triggers behavior P) Agent B (stimulus triggers behavior P) Topological differences lead to social differences 2.2 Trails - L. Steels, 1995 agents drop "radioactive crumbs" making trails an agent following a trail makes the trail faint until it disappears Reactive agents Stimulus
  • Slide 10
  • 2.3 Blackboard systems, Barbara Hayes-Roth, 1985 Blackboard = a common area (shared memory) in which agents can exchange information, data, knowledge Agents initiates communication by writing info on the blackboard Agents are looking for new info, they may filter it Agents must register with a central site for access authorization Blackboard = a powerful distributed knowledge paradigm Agents = Knowledge sources (KS) 10 Cognitive agents KS Control Blackboard events Pending KS Activations
  • Slide 11
  • 3. Direct communication Sending messages = method invocation The Actor language an Actor executes a sequence of actions in reply to the received message Exchange of partial plans distributed planning ACL = Agent Communication Languages communication as action - communicative acts 11
  • Slide 12
  • 3.1 Agent Communication Languages Concepts (distinguish ACLs from RPC, RMI or CORBA, ORB) : ACLs handle propositions, rules, and actions instead of objects with no associated semantics An ACL message describes a desired state in a declarative language, rather than a procedure or method invocation ACLs are mainly based on BDI theories: BDI agents attempt to communicate their BDI states or attempt to alter others BDI state ACLs are based on Speech Act Theory Agent behavior and strategy drive communication and lead to conversations 12 ACL Content language Ontology
  • Slide 13
  • Ontology =formal definition of a body of knowledge. The most typical ontology used in building agents involves a structural component. Essentially a taxonomy of class and subclass relations coupled with definitions and relationships between things. (Jim Hendler) An ontology is analogous to a data base organization, not the contents of the database. Example: To express the idea that a block is a physical object we might use the FOPL expression: x (Block x) (PhysicalObject x) To state relationships between classes: x,y,z (instanceOf x y ) (subclassOf y z) (instanceOf x z) To define a relationship On(X,Y) (domain On PhysicalObject) (range On PhysicalObject)
  • Slide 14
  • 14 Origins of ACLs Knowledge Sharing Effort - DARPA, 1990 External Interface Group - interaction between KBS - KQML Interlingua language for communicating between independent agents. KIF (not designed as a language to be used by humans) Shared, Reusable Knowledge Bases Ontolingua (set of tools written in Lisp for analyzing and translating ontologies. Uses KIF parser and syntax checker. Web-based)
  • Slide 15
  • Theory of Speech Acts J. Austin - How to do things with words, 1962, J. Searle - Speech acts, 1969 Treats communication as an action made to further agents intentions Changes world in a way analogous to physical actions Need formal representation so planning systems can reason about them. A speech act has 3 aspects: locution = physical utterance by the speaker illocution = the intended meaning of the utterance by the speaker (performative) prelocution = the action that results from the locution Alice told Tom: "Would you please close the door 15
  • Slide 16
  • 16 Human Communication: Intent may be ambiguous Colleague states I am cold What is the meaning? For computers, state performative (KQML) or Communicative Act (FIPA) so no ambiguity (except in content itself).
  • Slide 17
  • 17 Illocutionary aspect - several categories (According to speech act theory) oAssertives, which inform: the door is shut oDirectives, which request: shut the door, can pelicans fly? oCommissives, which promise something: I will shut the door oPermissive, which gives permission for an act: you may shut the door oProhibitives, which ban some act: do not shut the door oDeclaratives, which causes events: I name you king of Cache Valley oExpressives, which express emotions and evaluations: I am happy
  • Slide 18
  • KQML Knowledge Query and Manipulation Language A high-level, message-oriented communication language and protocol for information exchange, independent of content syntax (KIF, SQL, Prolog,) and application ontology KQML separates: semantics of the communication protocol (domain independent) semantics of the message (domain dependent) 3 (conceptual) layers 18 Content Communication Message Describes low level communication parameters: - identity of sender and receiver - a unique id associated with the communication Core of KQML - identity of the network protocol with which to deliver the message - speech act or performative Optional - content language - ontology
  • Slide 19
  • Syntax LISP-like list of attribute/value pairs (ask-one :sender joe :receiver ibm-stock :reply-with ibm-stock :language PROLOG // of content :ontology NYSE-TICKS // define terminology :content (price ibm ?price) ) 19 (tell:sender willie :receiver joe :reply-with block1 :language KIF :ontology BlockWorld :content (AND (Block A)(Block B) (On A B)) ) 1. Query performatives: ask-one, ask-all (want all answers to question), ask-if, stream- all (multiple response version of ask-all) (stream-all:sender willie :receiver ibm-stock :content (price ?VL ?price ) ) (standby :content (stream-all :content (price ?VL ?price) ) ask-one(P) tell(P) tell(P1) stream-all(P) tell(P2) eos tell(P1,P2,...) ask-all(P) B B B A A A
  • Slide 20
  • 20 4. Generic informational performatives: tell (I know it), untell, insert (add to your VKB), delete,... tell(P) untell(P) delete(P) insert(P) 2. Generator performatives: standby (be ready to respond), ready, next, rest, discard, generate,... 6. Network performatives: register, unregister, forward, route,... 3. Response performatives: reply, sorry... 5. Capability performatives: advertise, subscribe, recommend... Facilitator A A B B
  • Slide 21
  • 21 Knowledge Sharing Effort KSE Darpa funded in 1990 Resulted in KQML KIF (knowledge interchange format) looks like first order logic (and, or, forall, exists

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