Jade Slides

8/2/2019 Jade Slides

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Mehdi Dastani

Multi-Agent Systems


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What is JADE?JADE (Java Agent DEvelopment framework) is a FIPA compliantagent platform and a Java framework for the development of MAS.

The Jade platform is based on a middleware that facilitates thedevelopment of distributed multi-agent applications based on a peer-to-peer communication architecture.

The environment can evolve dynamically with agents that appear

and disappear in the system according to the needs and therequirements of the context.

JADE Project started in July 1998 as joint development of TelecomItalia Lab and Parma University. JADE is the Leading Open SourceFIPA compliant agent platform.

Currently JADE development is driven by a board composed of fiveindustrial partners:TILAB, Motorola, Whitestein Technologies AG,

Profactor GmbH, and France Telecom R&D.


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JADEAn agent platform that implements the basic services and infrastructureof a distributed multi-agent application:

agent life-cycle, agent mobility, and agent securitywhite & yellow-page services

peer-to-peer message transport & parsing ; also multi-partycommunicationscheduling of multiple agent tasksset of graphical tools to support monitoring, logging, and debugging

Some relevant features:Distributed Agent Platform

seen as a whole from the outside world

spanning multiple machinesenables interoperability through FIPA complianceTwo levels concurrency model

Inter-agent (pre-emptive, Java threads)

Intra-agent (co-operative, Behaviour classes)


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The architectural modelA JADE-based application is composed of a collection of active componentscalled Agents. Each agent has a unique name .

Each agent is a peer since he can communicate in a bidirectional way with allother agents

Each agent lives in a container (that provides its run time) and can migratewithin the platform

One container plays the role of main (where AMS, DF live)


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Agent class and namesA type of agent is created by extending the jade.core.Agent classand redefining the setup() method.

Each Agent instance is identified by an AID (jade.core.AID),composed of a unique name plus some addresses; the getAID()method of the Agent class

Agent names are of the form @ .The complete name of an agent must be globally unique. Thedefault platform name is :/JADE . Theplatform name can be set using the name option

Within a single JADE platform agents are referred through their

names only.Given the name of an agent its AID can be created as

AID id = new AID(localname, AID.ISLOCALNAME);

AID id = new AID(name, AID.ISGUID);


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import jade.core.Agent ;

public class HelloAgent extends Agent{

protected void setup (){

System.out.println("Hello World. ");System.out.println("My name is "+ getLocalName ());

}}

$> javac HelloAgent.java $> java jade.Boot fred:HelloAgent

This is JADE 3.0b1 .Hello World.

My name is fred

Hello World: A Simple Example


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Starting Agent ExecutionBirth of a new agent

The agent is given an identifier

It is registered with the AMSIt is put in the AP_ACTIVE stateIts setup() method is executed

The setup() method is therefore the point where anyapplication-defined agent activity starts

Initialise the agentAdd tasks using the method addBehaviour()

Scheduled as soon as the setup() method ends


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The Behaviour classThe actual job that an agent does is typically carried out withinbehavioursBehaviours are created by extending jade.core.behaviours.BehaviourclassTo make an agent execute a task it is sufficient to create an instance ofthe corresponding Behaviour subclass and call the addBehaviour ()method of the Agent class.

Each Behaviour subclass must implementpublic void action (): what the behaviour actually doespublic boolean done (): Whether the behaviour is finished

An agent can execute several behaviours in parallel, however,behaviour scheduling is not preemptive , but cooperative andeverything occurs within a single Java ThreadBehaviour switch occurs only when the action() method of the currentlyscheduled behaviour returns.


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import jade.core. Agent ;import jade.core. behaviours.* ;

public class myAgent extends Agent {

protected void setup () { addBehaviour ( new myBehaviour ( this ) ); }

class myBehaviour extends SimpleBehaviour {public void action () { //... the real programming !! }private boolean finished = false;public boolean done () { return finished; }} // ----------- End myBehaviour

} //end class myAgent

Hello World! My name is fred Hello World! My name is fred Hello World! My name is fred Hello World! My name is fred ..... loops until stopped with CTL-C.... !



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import jade.core. Agent ;import jade.core. behaviours.* ;

public class myAgent extends Agent {

protected void setup () { addBehaviour ( new myBehaviour ( this ) ); }

class myBehaviour extends SimpleBehaviour {int n=0;public void action () { ; n++; }public boolean done () { return n>=3; }

} // ----------- End myBehaviour

} //end class myAgent

Hello World! My name is fred Hello World! My name is fred

Hello World! My name is fred



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public class MyAgent extends Agent {protected void setup() {

System.out.println(Adding waker behaviour);addBehaviour(new WakerBehaviour(this, 10000) {

protected void handleElapsedTimeout() { // perform operation X

}

} );}

}

Operation X is performed 10 seconds after the Adding waker behaviour printout appears.

WakerBehaviour: A Simple Example


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public class tickeragent extends Agent { Behaviour loop;

protected void setup() { loop = new TickerBehaviour( this, 10000 ) {

protected void onTick() { // perform operation X

} }; addBehaviour( loop );

}

}

Operation X is performed periodically every 10 seconds.

TickerBehaviour: A Simple Example


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More about behavioursThe onStart () method of the Behaviour class isinvoked only once before the first execution of theaction() method.

The onEnd () method of the Behaviour class is invokedonly once after the done() method returns true.

The removeBehaviour () method of the Agent class canbe used to remove a behaviour from the agent pool ofbehaviours. The onEnd() method is not called.

When the pool of active behaviours of an agent isempty, the agent enters the IDLE state and its thread

goes to sleep


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Blocking or selecting

The block () method of the Behaviour class removes a behaviourfrom the agent pool of behaviours and puts it in a blocked state.

Each time a message is received all blocked behaviours areinserted back in the agent pool and have a chance to read andprocess the message.

It is possible to read only messages with certain characteristicsspecifying a jade.lang.acl.MessageTemplate parameter in thereceive () method.

The Agent class also provides the blockingReceive () method;there are overloaded versions that accept a MessageTemplateand/or a timeout.


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Blocking or selecting

public void action() {ACLMessage msg = myAgent.receive();if (msg != null) {

// Message received. Process it...

}else {

block();}}


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FIPA ACL Message Elements

p e r f o r m a t i v e What action the message performss e n d e r Initiator of the message

r e c e i v e r Recipient of the messager e p l y - t o Recipient of the message replyc o n t e n t Content of the messagel a n g u a g e Language used to express contente n c o d i n g Encoding used for contento n t o l o g y Ontology context for contentp r o t o c o l Protocol message belongs toc o n v e r s a t i o n - i d Conversation message belongs tor e p l y - w i t h Reply with this expressioni n - r e p l y - t o Action to which this is a replyr e p l y - b y Time to receive reply by


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ACL Message Example(request:sender (:name [email protected]:8080):receiver (:name rexhotel@tcp://hotelrex.com:6600)

:ontology personal-travel-assistant:language FIPA-SL:protocol fipa-request:content

(action movenpickhotel@tcp://movenpick.com:6600(book-hotel (:arrival 25/11/2000) (:departure 05/12/2000) ...)))

Any language can be used as a Content Language, e.g.:KIF, Prolog, SQL, Serialized Objects, Binary Large ObjectsFIPA-SL, FIPA-CCL, FIPA-RDF, FIPA-KIF


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Sending/receiving MessageACLMessage msg = receive(); ACLMessage reply = new ACLMessage( ACLMessage.INFORM ); reply.setContent( "Pong" ); reply.addReceiver( msg.getSender() );

send(reply);

public void action() { ACLMessage msg = receive();

if (msg!=null) { ...; ACLMessage reply = msg.createReply(); reply.setPerformative(ACLMessage.INFORM ); reply.setContent(" Pong" ); reply.send();

}block(); }


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DF (Directory Facilitator)


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Interacting with the DF Agent

The DF is an agent, it communicates using ACLThe ontology and language that the DF understandsare specified by FIPAThe jade.domain.DFService class provides static utility

methods that facilitate the interactions with the DFregister();modify();

deregister();search();

The JADE DF also supports a subscription mechanism


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DFDescription

formatWhen an agent registers with the DF it must providea description

The agent AIDA collection of service descriptions (class

ServiceDescription):The service type (e.g. Weather forecast)The service name (e.g. Meteo-1)The languages, ontologies and interaction protocols that mustbe known to exploit the serviceA collection of service-specific properties in the form key-valuepair

When an agent searches/subscribes to the DF itmust specify another DFAgentDescription that isused as a template


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Interacting with the DF Agentprotected void setup() {

...DFAgentDescription dfd = new DFAgentDescription();dfd.setName(getAID());

ServiceDescription sd = new ServiceDescription();sd.setType(book-selling);sd.setName(JADE-book-trading);dfd.addServices(sd);DFService.register(this, dfd);...

}

protected void takeDown() {DFService.deregister(this);

}


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Agent Management System

The authority in a JADE platform; all platformmanagement actions (creating/killing agents,

killing containers...)Other agents can request the AMS to performthese actions by using

The fipa-request interaction protocolThe SL languageThe JADE-Management ontology and relatedactions

getAMS () => the AID of the AMS


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The main graphical tools of JADE

Management, control, monitoring, and

debugging of a multi-agent platformRMA (Remote Monitoring Agent)Dummy AgentSniffer AgentIntrospector Agent

Log Manager AgentDF (Directory Facilitator) GUI


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AdvantagesNo need to implement the Agent Platform

AMS, DF executed at start-upNo need to implement agent-management ontology and

functionalitiesAn agent is registered with the Agent Platform within itsconstructor, it is given a name and an addressThe DFService class provides a simplified interface to access theservices of the DF (registration, searching, lease-renewal, )

No need to implement Message Transport and ParsingAutomatically (and possibly efficiently) done by the framework

when sending/receiving messagesInteraction Protocols must only be extended via handle methodsStandard FIPA !

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