Computer Science 25/06/20151 Agent Communications: Static Protocols CPSC /CPSC Rob Kremer Department of Computer Science University of Calgary

25/06/2015CPSC /599.68: Agent Communications2 Static (Ad-hoc) Protocols Merely “scripts” that the agent follows Typical notation is state diagrams Petri nets are a generalization of state diagrams

25/06/2015CPSC /599.68: Agent Communications3 Ad-hoc Protocols: Petri Nets Buyer: Request to BuySeller: Request PaymentSeller: Accepting to SellBuyer: Accepting to PayBuyer: Paying for itemSeller: Accepting PaymentSeller: Handing out itemBuyer: Accepting itemSuccess

25/06/2015CPSC /599.68: Agent Communications4 Simple Petri Nets “Place” “Transition” “Arc” Directed arcs only Strictly bipartite “Tokens” occupy places (a place can contain any number of tokens) A transition can fire only when there is sufficient tokens at all of the incoming places. The transition firing consumes tokens at the incoming side and emits tokens to the places on the outgoing side.

25/06/2015CPSC /599.68: Agent Communications5 Transitions If ALL of a transition’s incoming places have tokens, it MAY fire So if there’s a single token to available for more than one transition, only one of them MAY fire

25/06/2015CPSC /599.68: Agent Communications6 Transitions A transition will place tokens on all of it’s outgoing places IF it fires

25/06/2015CPSC /599.68: Agent Communications7 Transitions EVERY incoming place must have sufficient* tokens available in order for it to fire

25/06/2015CPSC /599.68: Agent Communications8 Transitions Places can contain any number of tokens

25/06/2015CPSC /599.68: Agent Communications9 Lots of other kinds of Petri Nets –Weighted Petri nets –Coloured Petri nets –Hierarchy –Vector addition system with states –Prioritised Petri nets –Timed Petri nets –Stochastic Petri nets –etc. Could do the whole course on Petri Nets! A decent quick description is on Wikipedia at

25/06/2015CPSC /599.68: Agent Communications10 Example: “call for proposals” A MIP-net (Multi-agent Interaction Protocol net) – combining two A-nets (Agent nets) and one IP- net (Interaction Protocol net). Reference: Sea Ling & Seng Wai Loke. A Formal Compositional Model of Multiagent Interaction. AAMAS’03 – International Conference on Autonomous Agents and Multi- Agent System, July 14-18, 2003, Melbourne, Australia. ACM, Also available: 000/860791/p1052- ling.pdf?key1=860791&key2= &coll=&dl=ACM&CFID= &CFTOKEN= /860791/p1052- ling.pdf?key1=860791&key2= &coll=&dl=ACM&CFID= &CFTOKEN= Ling & Loke 2003, p.1053

25/06/2015CPSC /599.68: Agent Communications11 Example: A produce Protocol This is an extension of colored Petri nets called “reference nets” Reference: Lawrence Cabac, Daniel Moldt & Heiko Rolke. A Proposal for Structuring Petri Net-Based Agent Interaction Protocols. Lecture Notes in Computer Science: 24th International Conference on Application and Theory of Petri Nets, Eindhoven, Netherlands, June Springer, Also available: hamburg.de/TGI/mitarbeiter/wimis/cabac/netcomponents.pdf.gzhttp:// hamburg.de/TGI/mitarbeiter/wimis/cabac/netcomponents.pdf.gz

25/06/2015CPSC /599.68: Agent Communications12 Issues Rigid and Brittle Hard to account for all eventualities See assignment 1 to convince yourself of this