Slide: 1

JADE Java Agent DEvelopment Framework

Fabio Bellifemine, CSELT - Torino (Italy)

Agostino Poggi, Giovanni Rimassa, University of Parma (Italy)

Slide: 2

What is JADE is a software framework

that simplifies the implementation of multi-agent systems

is the middle-ware for MAS target users: agent programmers for MAS agent services

life-cycle, white-page, yellow-page, message transport tools to support debugging phase

remote monitoring agent, dummy agent, sniffer agent designed to support scalability

(from debugging to deployment) from small scale to large scale

fully implemented in Java distributed under LPGL

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Network protocol stack

JRE 1.2 JRE 1.2 JRE 1.2

Jade Main-container Jade Agent Container Jade Agent Container

Jade distributed Agent Platform

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Host 1 Host 2 Host 3

Distributed architecture of a JADE Agent Platform

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Intra-Container Message Transport

(Java events)

White pageservice

AgentManagement

System

Yellow pageservice

DirectoryFacilitator

Agent Communication Channel

Inter-Containers Message Transport

(Java RMI)

Inter-Platforms Message Transport

(IIOP)

local cache of agent addresses

Internal architecture of the JADE main-container

Note: The internal architecture of a JADE container is similar, butit does not contain the AMS, the DF, and the IIOP modules.

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Mapping theory into design

Agents are autonomous.

Agents are social entities.

Messages are speech acts, not invocations.

An agent can say “no” and “I don’t care”.

Agents are active objects.

Intra-agent concurrency is needed.

Asynchronous messaging must be used.

Peer-To-Peer messaging (built over distributed objects Client/Server interactions).

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JADE Communication Sub-system every agent has a private queue of ACL

messages created and filled by the JADE communication sub-system

designed as a chameleon to achieve the lowest cost for message passing the mechanism is selected according to the situation the overheads depend on the receiver’s location and the

cache status

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JADE Communication Sub-system

Message Dispatcher

AGENT CONTAINER

Message Dispatcher

AGENT CONTAINER (FE)

Message Dispatcher

AGENT CONTAINER

Java RMI

Agent2

event

Localcache

AgentGlobalDescriptorTable

event Agent3

Agent1

AgentContainerTable

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Communication Model implications on the JADE implementation

library of interaction protocols

the framework directly supports parsing envelope parser (in JADE 2.0) ACL parser CL parser

including support for uuencoded Java serialization Ontology checker

the framework can be extended by the user support to define/save/load new ontologies interface for CLParser/Encoder automatically used by the framework

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Agent Execution Modelimplications on the JADE implementation

agent is autonomous it completely controls its thread of execution

private proxy of the life-cycle manager it decides itself when to read received messages and which messages to

read/serve the transport mechanism fills a private queue but it does not call the

agent code (no automatic callback)

agent needs concurrency can engage multiple simultaneous conversations can execute several concurrent tasks

Java multi-thread or/and JADE behaviours with cooperative scheduling

one thread-per-agent rather than one thread-per-task/convers.

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Int. architect. of a generic JADE agent

private inbox ofACL messages

scheduler ofbehaviours

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agent resources

beliefs

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…activeagent behaviours(i.e. agent intentions)

JADE library ofinteraction protocolsand of generic agent behaviours

The JADE framework includes a library of interaction protocolsand generic agent behaviours, that must be customized for the specificapplication needs in order to create the agent capabilities

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Concurrency in JADE different containers on the same platform

1 JVM per container

different agents on the same container run in a preemptive multi-threaded environment scheduled by the JAVA

Virtual Machine

different behaviours on the same agent scheduled cooperatively

every behaviour must release the control to allow the other behaviours to be executed

no stack to be saved, more effort to the programmer JADE scheduler carries out a round-robin non-preemptive policy among

all behaviours in the ready queue Behaviours can be composed into a tree

every Behaviour is a Finite State Machine one state per execution time slot

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Behaviour-based Concurrency Model

Multithreaded inter-agent scheduling.

Behaviour abstraction Composite for structure Chain of Responsibility for

scheduling. No context saving.

x:SequentialBehaviour y:SequentialBehaviour

x1:SimpleBehaviour x2:SimpleBehaviour y1:SimpleBehaviour y2:SimpleBehaviour

1 2

:Agent

1.1 1.2 2.1 2.2

run()

mainLoop()

b1 = schedule()

Exc. handler

run()

mainLoop()

Exc. handler

run()

mainLoop()

Exc. handler

run()

mainLoop()

b2 = schedule()

Exc. handler

b1.action() b1.done()?

a) b) c) d)

run()

mainLoop()

Exc. handler

run()

mainLoop()

Exc. handler

b2.action() b2.done()?

e) f)

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Scalability in JADE

Configuration of a platform from one MAS on a single host

single-host platform to one agent on a single host

agent platform on a cluster of hosts configuration can be changed at run-time

hot restarting is possible thanks to the local caches agent is referred by name => no need to get new reference

The agent container front end is the bottle-neck but it is involved only when strictly necessary

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JADE 1.25 main features

Fipa compliance tested at Seoul + more library of interaction

protocols a number of DFs can be

instantiated And

core is less than 250 KB (not compressed)

intra-platform agent mobility

supporting tools: RMA, DummyAgent, Sniffer

integrated with Jess

support for registration (and automatic usage) of user-defined CL and ontologies

library of common behaviours (e.g. WakerBehaviour) that can be composed

usability installing / sw requirements

1 jar file, JRE 1.2 programming

about 10 public classes + the library of IPs and behaviours

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Current usage of JADE FACTS

TV-based entertainment CSELT, NHK, Imperial College of London, IRST

personal travel assistant BT, France Telecom, Broadcom

DICEMAN - Trading of A/V content CSELT, KPN, Starlab, Politecnico of Torino

FILIGRANE - e-commerce of mobile agents LiMe - Living Memory for connected communities

ICL, Philips, Queen Margaret University College, DomusAcademy 2 day field trial for dynamic user profiling, collective information

dissemination and memory management Univ. Helsinki, Parma, Bologna, Brescia SONG, SAFIRA, COMMA, ...

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How much of FIPA is hidden by JADE to the programmer? no need to implement the Agent Platform

AMS, DF, and ACC executed at start-up

no need to implement agent-management ontology and functionalities an agent is registered with the AP within its constructor

it is given a name and an address the Agent class provides a simplified i/f to access the services of

the DF (registration, searching, …)

no need to implement Message Transport and Parsing automatically (and possibly efficiently) done by the framework

when sending/receiving messages

Interaction Protocols must only be extended via handle methods

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Open Source

JADE is now available in Open Source under LGPL license http://sharon.cselt.it/projects/jade

running platform available with AMS, DF, ACC successful test with Broadcom, Siemens, and University of

Parma

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JADE - what is next?

inter-platform agent mobility

plans (i.e. JADE behaviours) as production rule systems when <guard check> do <code body> transition

<enable/disable other plans>

more transport protocols (SMTP, HTTP, WAP)

JADE run time for mobile terminals

checking new user requirements

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Communication Overheads

Same container no remote invocations; ACL message object is cloned

Same Agent Platform, different container, cache hit one RMI call, the ACL message object is serialized and

unserialized by RMI run time Same Agent Platform, different container, cache miss

two RMI calls (update the cache, send the message), the ACL message object is serialized and unserialized by RMI run time

Different platforms CORBA remote invocation through IIOP double marshalling from Java object to Java String to IIOP

byte stream (sender side) double unmarshalling from IIOP byte stream to Java String

to Java object (receiver platform side) + the cost of delivering to the actual receiver agent

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Example of a Behaviour

public class my3StepBehaviour { private int state = 1; private boolean finished = false;

public void action() { switch (state) { case 1: { op1(); state++; return; } case 2: { op2(); state++; return; } case 3: { op3(); state=1; finished = true; return;

} } }

public boolean done() { return finished; }}

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Integration with JESS

In some cases agents may need to reason about the state of the world

JESS (Java Expert System Shell) is a symbolic reasoning tool it has been developed by Sandia National Laboratories it is free for non-commercial usage it is written in Java and it support simple integration into Java applications a built-in behaviour is available in the JADE library that, for each received

message, asserts a fact in the Jess engine that describe the message it allows reasoning about messages in JESS it allows a JESS program to control sending/receiving messages and/or

creating/destroying JADE behaviours

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JADE based applications are made by one or more Agents A JADE agent is mapped onto an user defined Java class,

that must subclass Agent class in jade.core package. Agent activities are mapped onto user defined subclasses

of Behaviour class in jade.core.behaviours package.

JADE Programming Model

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JADE Programming Model

The new JADE 1.4 supports user defined content languages and ontologies. Each agent holds a table of its capabilities. Message content is represented as instances of Frame

class, in a language independent way. User defined classes can be used to model ontology

elements (Actions, Objects and Predicates).

The new JADE 1.4 supports agent mobility. Intra-platform, weak mobility with on-demand class fetching.

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JADE Support Tools

Administration tools. RMA Management Agent.

White pages GUI. Agent life cycle

handling. Directory Facilitator GUI.

Yellow pages handling.

Development tools. DummyAgent.

Endpoint Debugger. Message Sniffer.

Man-in-the-middle.

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JADE Support Tools

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JADE 2.0

Released 12 September 2000 has been updated in order to comply with the new FIPA

specifications (so-called FIPA2000). unfortunatelly is has an impact on the user code

general improvements the GUI of the DF allows now to control a network of

federated yellow-page services programmer’s guide and examples

added a section with a guidelines to upgrade user code fixed all reported bugs improved the ontology and content language support

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FIPA2000

FIPA2000 is the new set of FIPA specifications that have been approved.

These specifications make relevant modifications to: Agent Platform Architecture and Management Message Encoding and Transport ACL and SL syntax

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Agent Management Model

The main difference is the ACC is not an agent.

The ACC supports the Message Transport System.

The Message Transport Service is the default communication method between agents on different APs.

The ACC also supports AP routing tasks.

Agent Platform

Agent Platform

AgentManagement

System

DirectoryFacilitator

Message Transport System

Agent

Software

Message Transport System

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Agent Naming

FIPA identifies an agent through an extensible collection of parameter-value pairs, called an Agent Identifier (AID). An AID comprises: A name. Other parameters, such as transport addresses, name resolution

service addresses, and so on.

The name of an agent is immutable; the other parameters in the AID of an agent can be changed.

A given agent may support many methods of communication and can put multiple transport address values in the :addresses parameter of an AID.

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Agent Management

Agent Management Ontology has some changes deriving from the introduction of agent AID representation and from the renaming of AMS and DF actions.

Now AMS and DF have a common subset of actions: register deregister search modify

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Message Structure

A message is made up of two parts: a message envelope expressing transport information, and a message body comprising the ACL message of the agent

communication.

For the purposes of message interpretation by an agent: ACL semantics are defined only over the ACL message

delivered in the message body of a FIPA message. All information in the message envelope is supporting

information only. How and if this information is used to by an agent for any kind of additional inference is undefined by FIPA.

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Message Transport Protocol

IIOP is no longer the sole message transport protocol.

Now there are three possible message transport protocol: IIOP WAP HTTP

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Message Encoding

String is no longer the sole message encoding.

Now there are three possible encoding: String encoding bit-efficient encoding XML

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Protocol and Encoding Mapping Each of the three message transport protocols

supports the three different kinds of message encoding.

Only the message envelope depends on transport protocol. Abstract Frame-based envelope syntax, mapped to

protocol-dependent concrete syntaxes.

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ACL and SL

ACL messages contains two new parameters: reply-to encoding

SL syntax has been modified to simplify content parsing.

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JADE 2.0

Version 2.0 upgrades JADE to be compliant to FIPA2000.

JADE 2.0 requires an upgrading phase of all the software written in earlier versions.

The main modifications are related to: Agent class ACLMessage class MessageTemplate class

Slide: 37

Agent class the agent name, that was a String, has been replaced by an

Agent Identifier, represented by the class AID.

In particular the name attribute is the globally unique identifier and, replaces the agent name of the previous version of JADE.

The methods getLocalName() and getName() continue to exist and work at the same way.

However the full name of an agent is no more composed of the concatenation of its local name and the platform IIOP address: now FIPA does not allow to distinguish between the local name and its home AP address.

A new method, getAID(), returns the agent AID.

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ACLMessage class

The new FIPA specifications have added the two new parameters reply-to and encoding to the ACL Message structure.

The specs have also removed the envelope parameter that is now treated separately.

The sender and receiver parameters do not contain any more, syntactically Strings, but AIDs.

As a consequence of that, the user code must be modified as follows.

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ACLMessage class

Replace

getSource() and setSource(String)

with

getSender() and setSender(myAgent.getAID()).

Replace

getDest, getFirstDest(), addDest()

with

getAllReceiver(), clearAllReceiver(),

addReceiver(AID), removeReceiver(AID).

getAllReceiver() returns an Iterator over all the receivers.

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ACLMessage class

ReplacesetReplyTo and getReplyTo

withsetInReplyTo and getInReplyTo.

This modification has been done to avoid ambiguity with the new reply-to parameter of FIPA.

ReplacesetEnvelope(String) and getEnvelope(String)

withaddUserDefinedParameter(":X-envelope", String),

getUserDefinedParameter(":X-envelope")

because envelope is no more a parameter of FIPA ACL Message .

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ACLMessage class

Take care of replying to messages by using the AID's in the reply-to parameter, when present, instead of those in the sender parameter.

The best practice is to use the method ACLMessage.createReply() that already takes care of that.

The deprecated method dump() has been removed, replace it with System.out.println(msg.toString()).

The deprecated method setType(String) has been removed, replace it with setPerformative(ACLMessage.REQUEST).