Computer Science CPSC /CPSC Rob Kremer Department of Computer Science University of Calgary 07/12/20151 Agent Communications

07/12/2015CPSC /599.68: Agent Communications2 What is an Agent? Autonomous Knowledge-based Reflective or Reactive Social

07/12/2015CPSC /599.68: Agent Communications3 What is an Agent? An agent Ag is a tuple Ag = (Sit,Act,Dat,f Ag ) where Sit is a set of situations Ag can be in Act is a set of actions Ag can perform Dat, Ag’s internal data, is the set of possible values Ag’s internal data areas can have f Ag : Sit  Dat  Act is the agents decision function From outside, Ag seems to be a “function” g Ag :Sit  Act There are lots of other models of agency; this one is usefully general

07/12/2015CPSC /599.68: Agent Communications4 Agents = Object? Both have internal data and receive messages xBut the object has no “choice” but to execute the method; the agent can decide if and what method to execute. objectagent method A method B method C message B method A method B method C sensor message B I might execute method B, or I might do nothing, or I might execute method C or ….

07/12/2015CPSC /599.68: Agent Communications5 Communicating Agents Traditional (low level) “Protocols” (eg: TCP/IP) are a bit simple… –They mostly deal with “here’s a message” Agents need a richer conversation space –Request/Reply, Offer/Reply, Subscribe/Inform Agents need to handle exceptional cases, complex interactions, and novel new interactions

07/12/2015CPSC /599.68: Agent Communications6 Simple Conversation: naive What time is it? It’s 2:00

07/12/2015CPSC /599.68: Agent Communications7 Simple Conversation: more complex What time is it? It’s 2:00 Just a sec, I’ll check Thanks

07/12/2015CPSC /599.68: Agent Communications8 Go ask someone else. Simple Conversation: failure What time is it? I don’t know, my watch stopped (didn’t hear)

07/12/2015CPSC /599.68: Agent Communications9 What do we need? Message format (syntax) Message semantics Interpretation of sequences of messages (conversations) –Message sequencing and turn-taking Conversation semantics

07/12/2015CPSC /599.68: Agent Communications10 Message Syntax Envelope/content Envelope can be read by all agents in the society Content is usually understood only by specialized agents

07/12/2015CPSC /599.68: Agent Communications11 Message Syntax performativethe type of the communicative act of the message senderthe sender of the message receiverthe intended recipients of the message reply-tosubsequent messages in this conversation thread are to be directed to the agent named contentthe content of the message; equivalently denotes the object of the action languagethe language in which the content parameter is expressed encodingthe specific encoding of the content field ontologythe ontology(s) used to give a meaning to the symbols in the content expression protocolthe interaction protocol that the sending agent is employing with this ACL message conversation-idan expression used to identify the sequence of communicative acts that form a conversation reply-withan expression that will be used by the responding agent to identify this message in-reply-toan expression that references an earlier action to which this message is a reply reply-bya time and/or date expression indicating the latest time the sending agent wants a reply

07/12/2015CPSC /599.68: Agent Communications12 Message Syntax: KQML-style ( request :act inviteToJoinCD :to casa:// /Bob :from casa:// /Alice :reply-with casa:// /Alice$$1453 :language casa.URL :language-version 1.0 :content casa:// /CDagent2 )

07/12/2015CPSC /599.68: Agent Communications13 Message Syntax: xml-style request inviteToJoinCD casa:// /Bob casa:// /Alice casa:// /Alice$$1453 casa.URL 1.0 casa:// /CDagent2

07/12/2015CPSC /599.68: Agent Communications14 Message Semantics Typically based on speech-act theory Performative is the main speech act FIPA implementation uses the performative and a BDI semantics

07/12/2015CPSC /599.68: Agent Communications15 Message Semantics: FIPA Performatives accept-proposalaccepting a previous proposal agreeagreeing to perform some action cancelinform another agent that the agent no longer need perform some action call-for-proposalcalling for proposals to perform an action confirminforms a given proposition is true disconfirminforms a given proposition is false failurean action was attempted but failed Informa given proposition is true inform-ifinform whether or not a proposition is true inform-refinform the object which corresponds to a descriptor not-understooddid not understand what the receiver just did propagatepass a message on proposesubmitting a proposal to perform an action proxypass on an embedded message query-ifasking whether or not a proposition is true query-refasking for the object referred to refuserefusing to perform an action reject-proposalrejecting a proposal during negotiation requestrequest to perform some action request-whenrequest to perform some action when some proposition becomes true request-wheneverrequest to perform some action each time the proposition becomes true subscriberequesting to notify of the value of a reference whenever the object changes

Message Semantics: FIPA request 07/12/2015CPSC /599.68: Agent Communications16 FP: FP (a) [i\j] ∧ B i Agent (j, a) ∧ ¬B i I j Done (a) RE: Done (a) FP(a) [i\j] denotes the part of the FPs of a which are mental attitudes of i.

Message Semantics: Social Commitments/CASA 07/12/2015CPSC /599.68: Agent Communications17

07/12/2015CPSC /599.68: Agent Communications18 Conversation Paradigms Ad-hoc protocols BDI (Belief, Desire, Intentions) Social Commitments

07/12/2015CPSC /599.68: Agent Communications19 Ad-hoc Protocols “Scripts” that the agent follows Issues: Rigid and Brittle. Hard to account for all eventualities

07/12/2015CPSC /599.68: Agent Communications20 Ad-hoc Protocols: Petri Nets

07/12/2015CPSC /599.68: Agent Communications21 BDI Belief –Environment Desire –Goals Intention –The current desire(s) chosen by the selection function with the beliefs and desires as input

07/12/2015CPSC /599.68: Agent Communications22 BDI Issues Sometimes end up with expressions like “I believe that you believe that I believe that you believe that…” Calls on agents to have a omniscient view of all the other agents FIPA is based on BDI semantics

07/12/2015CPSC /599.68: Agent Communications23 Social Commitments Many utterances imply some sort of “conversational” social commitment Eg: a request commits the receiver to reply Other social commitments are negotiated Eg: “wash my car” Basic Agent body: When an agent observes (or sends or receives) a message, it uses policies (rules) as social norms that generate (or delete) social commitments Agents spend their free time trying to fulfill the social commitments for which it is a debtor

07/12/2015CPSC /599.68: Agent Communications24 Social Commitments reply-propose-discharge(Alice,Bob,x) act(Bob,Alice,x) propose-discharge(Bob,Alice,x) Alice Bob request inform reply agree informack propose-discharge done reply informack reply-propose-discharge confirm reply informack reply(Bob,Alice,x) ack(Bob,Alice,x) ack ack(Bob,Alice,x) ack ack(Alice,Bob,x) ack ack(Alice,Bob,x) ack

07/12/2015CPSC /599.68: Agent Communications25 Social Commitments Issues Deals with complexity Agents make decisions based only on observable conversational moves (and the Environment and their internal state) Turn taking follows naturally