Participation Components for Holding Roles in MultiAgent Systems Protocols Christophe Sibertin-Blanc, IRIT Toulouse Nabil Hameurlain, LUPPIA Pau

21 oct. 2004, ESAW'04 2 Organisation-centred vs Individu-centred view on a MultiAgent vs System Accounting for engineering issues: Reusability, maintainability, interoperability, scalability … The system view: to ensure –Objectives –Rules –Tasks allocation –Resources sharing –Operation: security, performance, … The agent view: to allow – Desire, intention – Autonomy – Skills – Abilities – Openess, negociation, intensive interactions, …

21 oct. 2004, ESAW'04 3 Organisation-centred vs Individu-centred view on a MultiAgent vs System To conciliate the three perspectives, Separate the Concerns: the organisational features are treated as first-class entities at the specification, design and runtime levels => the organisational constraints are enforced => agents focus on their own functional concerns The interaction pattern: Protocols

21 oct. 2004, ESAW'04 4 Plan 1.The system view: Moderator Approach 2.The agent view: Participation Component 3.Example 4.Conclusion

21 oct. 2004, ESAW'04 5 The Moderator Approach: Protocols Items in the definition of a protocol: –Roles agents may hold –Types of interventions agents may perform –Initial state and final state –Casting constraints on the holding of roles –Behavior constraints on the performance of interventions A Conversation = a process following the rules of a protocol

21 oct. 2004, ESAW'04 6 The Moderator Approach: Architecture Moderator Functional Agent Library of Protocols Server of Conversations Functional agent direct contributor to the system’s goals, has the needed skill and abilities Moderator agent that monitor 1 conversation Grant roles to agents Manages the state of the conversation Receives and process the agents’ interventions Server of Conversation database on the available conversations and protocols Library of protocols Stores the definitions of protocols

21 oct. 2004, ESAW'04 7 Library of Protocols Server of Conversations (1) (3) (2) (3) (4) (5) (4) (5) The Moderator Approach: Operation (1) Asks for the creation of a new conversation (2) Looks for the protocol’s agent type (3) Instanciates a new moderator (4) Gives the moderator’s identity (5) Takes part in the conversation End : the Moderator terminates (5)

21 oct. 2004, ESAW'04 8 The Moderator Approach: properties System’s point of view: –The rules are respected Agents’ point of view: –They are relieved of watching over others –The interaction space is sure and well-defined –The interaction space is large

21 oct. 2004, ESAW'04 9 The Moderator Approach: what about the Agents’ autonomy? Agents autonomy consists in deciding: –Which conversation to initiate, and in which conversation to enter? –While taking part in a conversation, Which intervention and When? The effective use of this autonomy requires a deep knowledge of each protocol –Hard-coded into agent? NO –Declarative? –Delegated?

21 oct. 2004, ESAW'04 10 Plan 1.The system view: Moderator Approach 2.The agent view: Participation Component 3.Example 4.Conclusion

21 oct. 2004, ESAW'04 11 Participation Components: Principle To distinguish the strategic from the tactic knowledge Strategic knowledge: –has a large applicability, not bulky –must be kept by the agent, close to its own objectives Tactic knowledge: –specific to each role of each protocol, voluminous –delegated to a specific component: a Participation

21 oct. 2004, ESAW'04 12 Participation Components: architecture Library of Protocols Conversation Server (1) (4) (2) (3) (1) Asks for a role (2) Grants the role and creates a new participation (3) Strategic interactions (4) Tactic interactions End : the moderator terminates Participation Has the tactic knowledge to intervene in the conversation on the behalf of the functional agent

21 oct. 2004, ESAW'04 13 Participation Components: structure of a participation Strategic variables Tactic engine Role’s behavior AGENTMODERATOR The variables of the strategic kit The protocol’s behaviour constraints The strategy‘s operational semantics

21 oct. 2004, ESAW'04 14 Plan 1.The system view: Moderator Approach 2.The agent view: Participation Component 3.Example 4.Conclusion

21 oct. 2004, ESAW'04 15 Example: strategies of the bidder role in an auction Strategic choices: –to enter in an auction, if the good on sale matches the good wanted –the upper bound of bidding for that good firmly decidedbored basket -- thriftyhesitating wanted / proposed good adequation accepted financial effort

21 oct. 2004, ESAW'04 16 Example: strategic kit for the bidder role wanted: Goods;/object seeked adequacy_rate: Percentage /wanted--proposed matching (matching(wanted, o: Goods) > adequacy_rate): Boolean /enter in the auction for o? financing_rate: Percentage;/financing effort available_amount: Currency;/financial resources value(o: Goods): Currency; /evaluates of the price of o max_price: Currency; /the amount it is ready to pay

21 oct. 2004, ESAW'04 17 Example: The participation component /Agent type of the participation for the bidder role in a fish-market auction R_Agent Bidder_Fishmarket; object: Goods; max_price, p: Currency; RBTS R_to_bid ("OK") // to_pay (p) [p<=max_price] / to_bid() [p>max_price]/ newprice() R_new_price ("End") / object := Nul / p:= Current_price() R_to_pay (f)/ object := f R_newprice (p) / 0 12 for the bidder role in a fish-market auction R_to_bid(p) /

21 oct. 2004, ESAW'04 18 Conclusion The protocols' rules are strictly respected and agents have the means to exercise their autonomy within the remaining indeterminism Agents have access to a number of protocols, because strategic K has a large applicability and is not bulky Agents can have several concurent participations in conversations A methodology to design Protocols usable as resources Engineering issues: reusability, clear design, integrity, …