1. Institut für Softwarewissenschaft - Universität WienP.Brezany 1 Multi-Agent Systems A Modern Approach to Distributed Artificial Intelligence Peter Brezany

2. Institut für Softwarewissenschaft - Universität WienP.Brezany 2 Introduction and Definitions Intelligent Agents are relatively a new appearence in commercial applications. Their study began in the field of distributed artificial intelligence (DAI) vor 20 years. Definition: DAS is a field, which investigates systems where several (intelligent) entities cooperate to achieve one goal or to fulfill one common task. These entities are called agents and the field is called multi-agent systems (MAS). Currently several Java-based systems for the construction of MAS exist. Definition: An agent observes its environment by means of it sensors, and autonomously acts in this environment by means of its tools.

3. Institut für Softwarewissenschaft - Universität WienP.Brezany 3 An Agent in its Environment

4. Institut für Softwarewissenschaft - Universität WienP.Brezany 4 Attributes of an Intelligent Agent 1.Reaktivness – reaktion to changes in the environment is some time intervals to achieve its goal. 2.Proaktivness – to take initiative, goal-oriented behavior. 3.Social behavior – interraction with other agents to achieve their common goal.

5. Institut für Softwarewissenschaft - Universität WienP.Brezany 5 Agent Description : Example action : P A P - percept through sensors, A – action through effectors Condition-action rules

6. Institut für Softwarewissenschaft - Universität WienP.Brezany 6 Agent Description : Example (2) function SIMPLE-REFLEX-AGENT (percept) returns action static: rules // a set of condition-action rules env-state INTERPRET-INPUT(percept) rule RULE-MATCH(env-state, rules) action RULE-ACTION[rule] return action

7. Institut für Softwarewissenschaft - Universität WienP.Brezany 7 Simple Example if sensor (mailArrived) then effector (processMail)

8. Institut für Softwarewissenschaft - Universität WienP.Brezany 8 A Framework for Intelligent Agent Development Translation from the English original

9. Institut für Softwarewissenschaft - Universität WienP.Brezany 9 Mobile Agents

10. Institut für Softwarewissenschaft - Universität WienP.Brezany 10 Mobile Agent A mobile agent is an autonomous program that can migrate under its own control from machine to machine – on each machine, it interacts with service agents and other resources to accomplish its task. Below, an agent has migrated so that it can interact locally with a search engine and will migrate again to interact with additional search engines. Once the agent has the desired information, it will migrate one last time to return to its home site so that it can present the information to its owner.

11. Institut für Softwarewissenschaft - Universität WienP.Brezany 11 Introduction to the Topic Internet and mobile agents Think of the Internet as a distributed, massively parallel supercomputer that connects information repositories, databases, intelligent agents, and a mobile code. You can send your own personalized agents to roam the Internet. They will monitor your favorite Web sites, get you the ticket you couldnt get at the box office or help you to remotely schedule meetings for your overseas trip. The role of Java The advent of Java has truly revolutionized the Internet. It has created a global infrastructure that is just waiting for mobile agents to roam its wires and interact with millions od computers. (IBM Solution - Java Aglets)

12. Institut für Softwarewissenschaft - Universität WienP.Brezany 12 Introduction (2) Mobile agents have the unique ability to transport themselves from one system in a network to another. The ability to travel allows mobile agents to move to a system that contains services with which they want to interact and to take the advantage of being in the same host or network as the service (see the next figure). Mobile agents reduce network traffic and provide an effective means of overcoming network latency.

13. Institut für Softwarewissenschaft - Universität WienP.Brezany 13 Introduction (3) Mobile Agents Traveling from Computer to Computer

14. Institut für Softwarewissenschaft - Universität WienP.Brezany 14 What is a Java Aglet? Aglet = lightweight agent Generalization and extension of Java applets and servlets. Aglets are Java objects – mobile Java agents that can move from one host on the Internet to another. write once, run everywhere => write once, go everywhere An aglet that executes on one host can suddenly halt execution, dispatch itself to a remote host, and resume execution there. When the aglet moves, it takes along its program code as well as its data. Aglets are hosted by an Aglet server (see the next figure)

15. Institut für Softwarewissenschaft - Universität WienP.Brezany 15 Safe Hosting of Incoming Aglet

16. Institut für Softwarewissenschaft - Universität WienP.Brezany 16 What is the Aglet API? The Aglet API (Application Program Interface) is an agent development kit – in other words, a set of Java classes and interfaces that allows you to create mobile Java agents. The Aglets Software Development Kit (ASDK) is an implementation of the Aglet API that can be dowloaded from IBM Tokyo Research Laboratory´s Web site http://www.trl.ibm.com/aglets/idoagree103.htm.

17. Institut für Softwarewissenschaft - Universität WienP.Brezany 17 Several Good Reasons for Using MAs 1.They reduce the network load

18. Institut für Softwarewissenschaft - Universität WienP.Brezany 18 Several Good Reasons for Using MAs (2) 2. They execute asynchronously and autonomously.

19. Institut für Softwarewissenschaft - Universität WienP.Brezany 19 Several Good Reasons for Using MAs (3) 3. They overcome network latency – Critical real-time systems need to respond in real time to chnges in their environment. Controlling such systems throigh a factory network of a substantial size involves significant latencies – not acceptable in many cases. Solution: Mobile agents can be dispatched from a central controller to act locally and directly execute the controllers directions. 4. They adapt dynamically. Mas have the ability to sense their execution environment and react autonomously to changes. 5. They are naturally heterogeneous – they provide optimal conditions for seamless system integration. 6. They are robust and fault-tolerant – dynamic reaction to unfavorable situations and events; if a host is being shut down, all agents executing on that machine will be warned and can dispatch and continua their operation on another host in the network.

20. Institut für Softwarewissenschaft - Universität WienP.Brezany 20 Network Computing Paradigms

21. Institut für Softwarewissenschaft - Universität WienP.Brezany 21 Elements of a Mobile Agent System

22. Institut für Softwarewissenschaft - Universität WienP.Brezany 22 Agent The 2 fundamental concepts in the MA model: the agent and its execution environment – the place. A mobile agent is an entity that has 5 attributes (When an agent moves in the network it takes them with it): State: needed to resume computation after travelling. Implementation: needed for location-independent agent execution. Interface: needed for agent communication. Identifier: needed to recognize and locate traveling agents. Principals: needed to determine legal and moral responsibility (manufacturer, owner, etc).

23. Institut für Softwarewissenschaft - Universität WienP.Brezany 23 Agent Properties

24. Institut für Softwarewissenschaft - Universität WienP.Brezany 24 Place It is a context in which an agent can execute. 4 concepts play an important role in places: Engine : workhorse and virtual machine for one or more places Resources : databases, processors, and other services provided by the host Location : the network address of a given place Principals : those legally responsible for the operation of a place

25. Institut für Softwarewissenschaft - Universität WienP.Brezany 25 The Agent Model Pyramid

26. Institut für Softwarewissenschaft - Universität WienP.Brezany 26 Agent Behavior: Creation and Disposal An agent gets created in a place. The creation can be initiated either by another agent residing in the same place or by nonagent system outside the place. The creator is required to authenticate itself to the place, establishing the authority and credentials that the new agent will possess; initialization arguments for the agent can also be supplied. Creation involves three steps: –Instantiation and identifier assignment. –Initialization. –Autonomous execution. Disposing of an agent: –Preparing for disposal. –Suspension of execution

27. Institut für Softwarewissenschaft - Universität WienP.Brezany 27 Agent Behavior: Transfer The transfer process can be initiated by – the agent itself, –another agent residing in the same place, or –another agent or nonagent system outside the place. The agent is then dispatched from its current place (origin) and received by the specified place destination The origin place and the destination place manage the dispatch process. See the next slide!

28. Institut für Softwarewissenschaft - Universität WienP.Brezany 28 Agent Transfer

29. Institut für Softwarewissenschaft - Universität WienP.Brezany 29 Agent Class Transfer