1. Specifying Agent Interaction Protocols with AUML and OCL COSC 6341 Project Presentation Alexei Lapouchnian November 29, 2000

2. Background: Agents 1 An agent is a software-based computer system that has the following properties: -AUTONOMY: agents operate without the direct intervention of humans or others, and have some kind of control over their actions and internal state -SOCIAL ABILITY: agents interact with other agents (and possibly humans) via some kind of agent­communication language -REACTIVITY: agents perceive their environment and respond in a timely fashion to changes that occur in it -PRO-ACTIVENESS: agents don’t simply act in response to their environment, they are able to exhibit goal-directed behaviour by taking the initiative (usually through planning, BDI implementations)

3. Background: Agents 2 Applications: Agents can be used as intelligent controllers (British Telecom, Nortel), shopping agents (Compaq’s WebL), wrappers for some info sources, legacy software, etc. Inter-Agent Communication: allows to exchange knowledge despite differences in h/w platforms, OS’s, architectures, PL’s, knowledge representation and reasoning systems  very important  need for agent communication language (KQML, FIPA ACL)  speech acts, performatives (inform, request, accept, reject, commit, advertise, propose, etc.)  need for ontologies

4. Background: MAS Multi-Agent System is a community of (independent) agents.  Usually asynchronous, concurrent communications  Centralized/brokered or decentralized, dynamic or static  Agents playing multiple roles (supplier/creditor)  Complicated belief-desire-intention revision mechanisms in presence of inter-agent communication  Agents can take initiative and have control over whether and how they process external requests (unlike objects)  A lot of social aspects (e.g. trust, team work)

5. Agent Interaction Protocols AIP – communication pattern with an allowed sequence of messages between agents playing certain roles, constraints on the content of the messages, and semantics that is consistent with performatives within this pattern  constrains the parameters of the message exchange – types and order of messages, allows to detect illegal/incomplete conversations  specific class of software design patterns – describes problems that occur frequently in multiagent systems – and shows the core of reusable solutions to those problems AIPs: Contract Net, English Auction, Dutch Auction, Subscribe, etc.

6. Agent UML  Proposed UML extension for modeling agent-based systems  Agents are more complicated than objects – plain UML is insufficient for modeling agents and agent-based systems  Additional requirements: extended notion of roles, concurrency, mobile agents, agent cloning  Layered approach to protocols: overall protocol, interactions among agent, internal agent processing  AUML proposes new diagram type – Protocol diagram with Agent Lifelines and threads of interaction

8. Figure 2. Using packages to express nested protocols Figure 3. Recommended extensions for concurrency: a) AND b) OR c) XOR

9. Object Constraint Language OCL is part of UML specification and can be used to:  specify invariants on classes and types in UML class model  describe pre- and post- conditions on Operations and Methods  describe Guards  specify constraints on operations  specify the well-formedness rules of UML OCL has many built-in types including collection types (bag, set, sequence), enumerated type. It has many operations on collections: select, reject, forAll, exists, etc. context Company inv: self.employee->foAll(e1, e2 | e1 <> e2 implies e1.employeeNo <> e2.employeeNo)

10. OCL 2 Specifying postconditions in OCL: context Person::birthdayHappens() post: age = age@pre + 1 Constraints: AUML does not propose specifying AIP constraints, pre- and post- conditions formally -Need to specify additional constraints on protocols (e.g in auctions) -Possibility of expressing belief base changes -Useful when combining AIPs

11. Project Project goals: Model a multi-agent application with contract net protocol using Agent UML and specify constraints on AIP using OCL