Specifying Agent Interaction Protocols with AUML and OCL COSC 6341 Project Presentation Alexei Lapouchnian November 29, 2000
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)
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
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)
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.
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
Figure 2. Using packages to express nested protocols Figure 3. Recommended extensions for concurrency: a) AND b) OR c) XOR
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)
OCL 2 Specifying postconditions in OCL: context Person::birthdayHappens() post: age = + 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
Project Project goals: Model a multi-agent application with contract net protocol using Agent UML and specify constraints on AIP using OCL