AI-MAS 3.12.2004

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AI-MAS3.12.2004
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JADE

• An agent platform that implements the basic
  services and infrastructure of a distributed
  multi-agent application
• agent life-cycle and agent mobility
• white yellow-page services
• peer-to-peer message transport parsing also
  multi-party communication
• agent security
• scheduling of multiple agent tasks
• set of graphical tools to support monitoring,
  logging, and debugging
• encourages the development of pro-active
  applications
• Some relevant features
• is extremely light-weight, ported to
  J2ME-CLDC-MIDP 1.0 mobile terminals
• enables interoperability through FIPA compliance
• is an open source project originated by TILAB and
  currently governed by an International Board
• is used by several RD projects

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The architectural model

• A JADE-based application is composed of a
  collection of active components called Agents
• Each agent has a unique name
• Each agent is a peer since he can communicate in
  a bidirectional way with all other agents
• Each agent lives in a container (that provides
  its run time) and can migrate within the platform
• One container plays the role of main (where AMS,
  DF live)
• The main-container can be replicated via
  replication service

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Agent class and names

• A type of agent is created by extending the
  jade.core.Agent class and 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 ltlocal-namegt_at_ltplatform
  -namegt
• The complete name of an agent must be globally
  unique.
• The default platform name is ltmain-hostgtltmain-por
  tgt/JADE
• The platform 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)
• It is possible to pass arguments to an agent the
  getArguments() method
• An agent terminates when its doDelete() method is
  called.
• On termination the agents takeDown() method is
  invoked (intended to include clean-up operations).

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The Behaviour class

• The actual job that an agent does is typically
  carried out within behaviours
• Behaviours are created by extending the
  jade.core.behaviours.Behaviour class
• To make an agent execute a task it is sufficient
  to create an instance of the corresponding
  Behaviour subclass and call the addBehaviour()
  method of the Agent class.
• Each Behaviour subclass must implement
• public void action() what the behaviour actually
  does
• public boolean done() Whether the behaviour is
  finished
• An agent can execute several behaviours in
  parallel, however, behaviour scheduling is not
  preemptive, but cooperative and everything occurs
  within a single Java Thread
• Behaviour switch occurs only when the action()
  method of the currently scheduled behaviour
  returns.

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Behaviour types

• One shot behaviours.
• Cyclic behaviours.
• Complex behaviours.
• WakerBehaviour
• The action() and done() method are already
  implemented so that the onWake() method (to be
  implemented by subclasses) is executed after a
  given timeout
• After that execution the behaviour completes.
• TickerBehaviour
• The action() and done() method are already
  implemented so that the onTick() (to be
  implemented by subclasses) method is executed
  periodically with a given period
• The behaviour runs forever unless its stop()
  method is executed

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More about behaviours

• The onStart() method of the Behaviour class is
  invoked only once before the first execution of
  the action() method.
• The onEnd() method of the Behaviour class is
  invoked only once after the done() method returns
  true.
• Each behaviour has a pointer to the agent
  executing it the protected member variable
  myAgent
• The removeBehaviour() method of the Agent class
  can be used to remove a behaviour from the agent
  pool of behaviours. The onEnd() method is not
  called.
• When the pool of active behaviours of an agent is
  empty the agent enters the IDLE state and its
  thread goes to sleep

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ACLMessage

• Based on asynchronous message passing
• Message format defined by the ACL language (FIPA)
• Messages exchanged by agents are instances of the
  jade.lang.acl.ACLMessage
• Sending a message creating an ACLMessage object
  and calling the send() method of the Agent class
• Reading messages from the private message queue
  is accomplished through the receive() method
• Provide accessor methods to get and set all the
  fields defined by the ACL language
  get/setPerformative(), get/setSender(),
  add/getAllReceiver(), get/setLanguage(),
  get/setOntology(), get/setContent()

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Blocking or selecting

• The block() method of the Behaviour class removes
  a behaviour from the agent pool and puts it in a
  blocked state (not a blocking call!!). Each time
  a message is received all blocked behaviours are
  inserted back in the agent pool and have a chance
  to read and process the message.
• To avoid this it is possible to read only
  messages with certain characteristics specifying
  a jade.lang.acl.MessageTemplate parameter in the
  receive() method.
• The Agent class also provides the
  blockingReceive() method there are overloaded
  versions that accept a MessageTemplate and/or a
  timeout.

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FIPA Message Structure
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FIPA ACL Message Elements

• p e r f o r m a t i v e What action the message
  performs
• s e n d e r Initiator of the message
• r e c e i v e r Recipient of the message
• r e p l y - t o Recipient of the message reply
• c o n t e n t Content of the message
• l a n g u a g e Language used to express
  content
• e n c o d i n g Encoding used for content
• o n t o l o g y Ontology context for content
• p r o t o c o l Protocol message belongs to
• c o n v e r s a t i o n - i d Conversation
  message belongs to
• r e p l y - w i t h Reply with this expression
• i n - r e p l y - t o Action to which this is a
  reply
• r e p l y - b y Time to receive reply by

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ACL Message Example

• (request
• sender (name dominicagent_at_whitestein.com8080)
• receiver (name rexhotel_at_tcp//hotelrex.com6600)
  
• ontology personal-travel-assistant
• language FIPA-SL
• protocol fipa-request
• content
• (action movenpickhotel_at_tcp//movenpick.com6600
• (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 Objects
• FIPA-SL, FIPA-CCL, FIPA-RDF, FIPA-KIF

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Communicative Act Library

• accept-proposal accept a previously submitted
  proposal
• agree agree to perform some action, possibly in
  the future
• cancel cancel some previously requested action
• cfp make a cal for proposals to perform a given
  action
• confirm inform a receiver that a given
  proposition is true
• disconfirm inform a receiver that a given
  proposition is false
• failure inform another agent that an action was
  attempted but failed
• inform inform a receiver that a given
  proposition is true
• not-understood informs a receiver that sender
  did not understand
• query-if ask another agent whether a given
  proposition is true
• request requests a receiver to perform some
  action

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Communicative Act Library

• propose submit a proposal to perform a certain
  action
• query-ref ask another agent for the object
  referred to by a referential expression
• refuse refuse to perform a given action
• reject-proposal reject a proposal during a
  negotiation
• request-when request a receiver to perform some
  action when some given proposition becomes true
• request-whenever request a receiver to perform
  some action as soon as some proposition is true
  and thereafter each time the proposition becomes
  true again
• subscribe a persistent intention to notify the
  sender of a value, and to notify again whenever
  the value changes
• propagate the receiver treats the embedded
  message as sent directly to it, and must identify
  the agents denoted by the given descriptor and
  send the received propagate message to them
• proxy the receiver must select target agents
  denoted by a given description and to send an
  embedded message to them

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Interaction protocols

• Jade automatically handles the flow of messages
  and the timeouts
• callback methods that should be redefined to take
  the necessary actions
• jade.proto package contains behaviours for both
  the initiator and responder role (FIPA-Request,
  FIPA-Contract-Net, FIPA-Subscribe)
• Other FIPA IPs FIPA-Query, FIPA-Request-When,
  FIPA-AIterated-Contract-Net, FIPA-Auction-English,
  FIPA-Auction-Dutch, FIPA-Brokering,
  FIPA-Recruiting, FIPA-Propose

• Predefined sequences of messages exchanged by
  agents during a conversation

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Handling content expressions

• Creating the Ontology (domain specific)
• Defining the schemas ontology elements
• Defining the corresponding Java classes
• Handling content expressions as Java objects
• Using the ContentManager to fill and parse
  message contents
• Ontologies can be created with Protégé (with the
  beangenerator plugin)

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The Content Reference Model
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DF (Directory Facilitator)
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Interacting with the DF Agent

• The DF is an agent, it communicates using ACL
• The ontology and language that the DF
  understands are specified by FIPA
• The jade.domain.DFService class provides static
  utility methods that facilitate the interactions
  with the DF
• register()
• modify()
• deregister()
• search()
• The JADE DF also supports a subscription mechanism

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DFDescription format

• When an agent registers with the DF it must
  provide a description
• The agent AID
• A 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 must be known to exploit the
  service
• A collection of service-specific properties in
  the form key-value pair
• When an agent searches/subscribes to the DF it
  must specify another DFAgentDescription that is
  used as a template

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Agent Management System

• The authority in a JADE platform all platform
  management actions (creating/killing agents,
  killing containers...)
• Other agents can request the AMS to perform these
  actions by using
• The fipa-request interaction protocol
• The SL language
• The JADE-Management ontology and related actions
• getAMS() gt the AID of the AMS

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Mobility

• Hard mobility
• Status an agent can
• stop its execution on the local container
• move to a remote container (likely on a different
  host)
• restart its execution there from the exact point
  where it was interrupted.
• Code If the code of the moving agent is not
  available on the destination container it is
  automatically retrieved on demand.
• An agent must be Serializable in order to be able
  to move
• Mobility can be
• self-initiated through doMove() of the Agent
  class
• forced by the AMS (following a request from
  another agent)
• Agent cloning is also available - method
  doClone()

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Security

• Add-on that prevents the threats (malicious kill
  or shutdown, sniffing or tampering the messages)
  by providing support for
• Authentication and authorization
• End-to-end message integrity and confidentiality
• All security related API are embedded into the
  SecurityHelper
• Signing, encryption
• Policy files per user Platform, Container, AMS,
  Agent, Message

ACLMessage msg new ACLMessage(ACLMessage.INFORM)
...... SecurityHelper myHelper
(SecurityHelper) getHelper("jade.core.security.Sec
urity") myHelper.setUseSignature(msg) send(msg)

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Advanced features

• Using JADE (i.e. creating a container and
  starting agents) from an external Java program
  (servlets, applets, JSP..)
• Executing a normal JADE behavior in a dedicated
  thread
• Saving and reloading agent state on relational DB
  (persistence based on www.hibernate.org) add-on
• Integration with JESS (Java Expert System Shell)
• it allows reasoning about messages in JESS
• it allows a JESS program to control
  sending/receiving messages and/or
  creating/destroying JADE behaviours
• Distributed security, fault tolerance, support
  for replicated agents and services
• Protégé, XML, RDF and OWL
• Application-specific persistent delivery filters
  JADE kernel-level services
• The LEAP add-on

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LEAP

• JADE agents on PDA and mobile phones
• JADE-LEAP (J2SE, PJava, MIDP) different internal
  implementation, same APIs for agents
• JADE-LEAP for MIDP is itself a MIDlet the main
  class is jade.MicroBoot
• A MIDlet must be packaged as a single JAR file gt
  mix library app. Classes
• MIDP configuration parameters are specified in
  the JAD/manifest of the MIDlet
• Minimize target (ant) obfuscator 450 k -gt
  30-150 k
• Logging - uniform way (jade.util.Logger class)
• J2SE JAVA Logging
• PJava System.out.println()
• MIDP RecordStore

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The main graphical tools of JADE

• Management, control, monitoring, and debugging of
  a multi-agent platform
• RMA (Remote Monitoring Agent)
• Dummy Agent
• Sniffer Agent
• Introspector Agent
• Log Manager Agent
• DF (Directory Facilitator) GUI

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Advantages

• No need to implement the Agent Platform
• AMS, DF executed at start-up
• No need to implement agent-management ontology
  and functionalities
• An agent is registered with the Agent Platform
  within its constructor, it is given a name and an
  address
• The DFService class provides a simplified
  interface to access the services of the DF
  (registration, searching, lease-renewal, )
• 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
• Standard FIPA !

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Roadmap
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Links

• http//jade.cselt.it
• http//www.fipa.org
• http//www.hibernate.org
• http//herzberg.ca.sandia.gov/jess/
• http//protege.stanford.edu/
• www.swi.psy.uva.nl/usr/aart/beangenerator
• http//jadex.sourceforge.net