introduction of java agent development environment (jade) 余萍 [email protected]
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Outline
Introduction Foundation for Intelligent Physical Agents (FIPA) Java Agent Development Environment (JADE)
Running JADE Platform Install JADE Platform Run JADE Platform Run Agent on JADE Platform
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Foundation for Intelligent Physical Agents (FIPA)
IEEE Computer Society standards organization A body for developing and setting computer
software standards for heterogeneous and interacting agents and agent-based systems.
http://www.fipa.org/ A software agent
A piece of software that acts for a user or other program in a relationship of agency
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Within the scope of FIPA
Agent Lifecycle Management Message Transport Message Structure Inter-agent Interaction Protocols Ontologies Security
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The FIPA Agent Platform
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Agent Management
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Agent Management
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Sample DF Description
(df-agent-description:name (agent-identifier :name [email protected]
:addresses (sequence iiop://foo.com/acc))
:protocols fipa-request:ontologies (set fipa-agent-management):languages (set fipa-sl0):lease-time +00000000T600000000T)
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Message Transport
Agent message transport comprises two levels: (1) The Message Transport Protocol (MTP)
carries out the physical transfer of messages between two ACCs.
(2) The Message Transport Service (MTS) is provided by the AP to which an agent is attached. The MTS supports the transport of FIPA ACL messages between agents on any given AP and between agents on different APs.
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FIPA Conceptual model of an Agent Platform
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Agent Platform
Service
White page service
Life cycle ManagementAgent-Software Integration
Ontology Service
Human Agent Interaction
provides
Yellow page service
Message Transport service
Normative services Optional services
FIPA Message Structure
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Java Agent Development Framework
JADE is an enabling technology, a middleware for the development and run-time execution of peer-to-peer applications which are based on the agents paradigm and which can seamless work and interoperate both in wired and wireless environment. distributed system topology with peer-to-peer
networking software component architecture with agent
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JADE Features
FIPA-compliant distributed agent platform which can be split onto several hosts.
Java Application Programmer’s Interface. Library of FIPA interaction protocols,
such as Contract Net, ready to be used. Graphical User Interface to manage
several agents from the same Remote Management Agent.
Available at http://jade.tilab.com Latest version: Jade 4.3 (29/03/2013) JADE is free software and is distributed by Telecom Italia
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JADE Application Fields
Mobile Applications Internet Applications Corporate Applications Machine-to-Machine Applications
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JADE Platform
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Network protocol stack
JRE JRE JRE
Jade Main-container
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Jade Agent Container Jade Agent Container
Jade distributed Agent PlatformA
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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, HTTP, …)
cache of agent addresses
Directory Facilitator (DF)
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Directory Facilitator (DF)
Provides a Yellow Pages service by means of which an agent can find other agents providing the services he requires in order to achieve his goals.
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Agent Management System (AMS)
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Agent Management System (AMS)
Provides the naming service Ensures that each agent in the platform
has a unique name Represents the authority in the
platform To create/kill agents on remote
containers by requesting that to the AMS
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Remote Monitoring Agent (RMA)
Provide the GUI to control agents’ lifecycle
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Agent Life Cycle
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Message Transport System
Agent Communication Channel (ACC) Agent to Agent Agent Platform to 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, HTTP, …)
cache of agent addresses
JADE - Message Transport Service
controls the agent’s private queue of ACL messages designed as a chameleon
the transport mechanism is selected according to the situation▪ to achieve the lowest cost for message passing▪ the overheads depend on the receiver’s location and the cache
status distributed Agent Communication Channel
the main container is not a bottle-neck, thanks to the distributed caches
Message Transport Protocols (MTP) can be activated/deactivated at run-time on any container via the GUI▪ IIOP based on the ORB implementation of Sun▪ IIOP based on the ORBacus implementation ▪ allows to make persistent the object reference▪ allows a more friendly URL-format
corbaloc:iiop:hostname:port/name▪ HTTP MTP provided by EPFL under LGPL
multiple ACL encodings have been implemented▪ String-based, XML-based (EPFL), bit-efficient (Sonera)
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Agent Execution Model agent is autonomous
it completely controls its thread of execution has a private proxy of the life-cycle manager
decides itself when to read messages and which messages to read 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/conversation. Programming Model
A JADE agent is mapped onto an user defined Java class, that must subclass Agent class in jade.core package.
Agent tasks are mapped onto user defined subclasses of Behaviour class in jade.core.behaviours package.
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Agent Communication Model
Agents send/receive Java objects, that represent ACLMessages, within the scope of interaction protocols JADE hides all message coding (encoding/parsing)▪ Envelope level▪ String-based, XML-based
▪ Agent Communication Language level▪ String-based, XML-based, bit-efficient
▪ Content Language level▪ FIPA SL-0 + API to register user-defined content languages▪ support for Base64-encoded direct Java object serialization
▪ Ontology level▪ FIPA-Agent Management; JADE Agent Management▪ API to register user-defined content languages
▪ the framework can be extended by users▪ all levels provide APIs to implement/register new codecs▪ work is in progress to improve CL and ontology level extendibility
JADE provides a library of common interaction protocols▪ users just need to implement the handle methods▪ users can compose agent tasks like super-states of FSM
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Agent mobility
JADE supports intra-platform mobility and cloning A platform can be distributed across multiple hosts▪ each host is an agent container
Agents can migrate between containers Agents can clone across containers Self-initiated▪ doMove(Location) / doClone(Location, String)▪ before/afterMove() before/afterClone()
Requested to the platform (via the AMS)▪ Fipa-request interaction protocol▪ jade.domain.MobilityOntology defines all the concepts and
actions needed to support agent mobility and cloning
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Some graphical tools to support development
RMA (Remote Monitoring Agent) to browse the white-page service to control the agent life-cycle (e.g. remote creation, agent
migration, …) to activate/deactivate MTPs on containers to browse white-page services of remote agent platforms
DF GUI to browse the yellow-page service to make DF federations and browse remote DF’s
DummyAgent send/receive store/save ACLMessages
Sniffer Agent to sniff, debug, save to file, multi-agent conversations
Introspector Agent to debug an agent: queue of sent/received messages, queue of
behaviours, …
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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
Is the main-container a bottle-neck? the Agent Communication Channel is distributed the main container is involved only when strictly
necessary
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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 automatically launched at start-up
no need to implement agent-management ontology and functionalities an agent is registered with the AP by the Java constructor itself▪ it is given a name and an address
the Agent class provides a simplified interface 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 no need to implement Interaction Protocols
they must only be extended via handle methods
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Example Book Seller & Book Buyer
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Seller1
Seller2Buyer
Agent Communication Language
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Agent Communication Language
sender of the message list of receivers communicative intention (or “performative”) content content language ontology some fields
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Agent Communication Language
Receiving Messages
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An Example of Sender
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An Example of Receiver
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BookSellerAgent
BookSellerAgent extends Agent import jade.core.Agent; Initial process▪ Setup()▪ addBehaviour(new OfferRequestsServer());▪ addBehaviour(new PurchaseOrdersServer());
Agent Behaviour▪ import jade.core.behaviours.*;▪ PurchaseOrdersServer extends CyclicBehaviour▪ OfferRequestsServer extends CyclicBehaviour
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BookSellerAgent Setup()
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Service Registration• Service Name• Service Type
Add Behaviour
BookSellerAgent Takedown()
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Service deregistration
class Behaviour
This abstract class provides an abstract base class for modelling agent tasks, and it sets the basis for behaviour scheduling as it allows for state transitions (i.e. starting, blocking and restarting a Java behaviour object).
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class Behaviour (Cont.)
class SimpleBehaviour This abstract class models simple atomic behaviours. Its
reset() method does nothing by default, but it can be overridden by user defined subclasses.
class OneShotBehaviour▪ This abstract class models atomic behaviours that must be executed
only once and cannot be blocked. So, its done() method always returns true.
class CyclicBehaviour▪ This abstract class models atomic behaviours that must be executed
forever. So its done() method always returns false.
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BookSellerAgent OneShotBehaviour()
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BookSellerAgent CyclicBehaviour()
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class Behaviour (Cont.)
class WakerBehaviour This abstract class implements a one-
shot task that must be executed only once just after a given timeout is elapsed.
class TickerBehaviour This abstract class implements a cyclic
task that must be executed periodically.
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class Behaviour (Cont.) class CompositeBehaviour
This abstract class models behaviours that are made up by composing a number of other behaviours (children). So the actual operations performed by executing this behaviour are not defined in the behaviour itself, but inside its children while the composite behaviour takes only care of children scheduling according to a given policy.
class SequentialBehaviour▪ This class is a CompositeBehaviour that executes its sub-
behaviours sequentially and terminates when all sub-behaviours are done. Use this class when a complex task can be expressed as a sequence of atomic steps (e.g. do some computation, then receive a message, then do some other computation).
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class Behaviour (Cont.)
class ParallelBehaviour▪ This class is a CompositeBehaviour that executes its sub-behaviours
concurrently and terminates when a particular condition on its sub-behaviours is met. Proper constants to be indicated in the constructor of this class are provided to create a ParallelBehaviour that ends when all its sub-behaviours are done, when any one among its sub-behaviour terminates or when a user defined number N of its sub-behaviours have finished. Use this class when a complex task can be expressed as a collection of parallel alternative operations, with some kind of termination condition on the spawned subtasks.
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class Behaviour (Cont.)
class FSMBehaviour▪ This class is a CompositeBehaviour that executes its children
according to a Finite State Machine defined by the user. More in details each child represents the activity to be performed within a state of the FSM and the user can define the transitions between the states of the FSM. When the child corresponding to state Si completes, its termination value (as returned by the onEnd() method) is used to select the transition to fire and a new state Sj is reached. At next round the child corresponding to Sj will be executed. Some of the children of an FSMBehaviour can be registered as final states. The FSMBehaviour terminates after the completion of one of these children.
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实习题
基于Aglets或 Jade开发一个电子集市应用，集市中有三类角色，分别为Manager， Seller，Buyer。其中，Manager负责对集市中的交易进行管理， Seller是电子集市中的交易的提供方， Buyer是电子集市中交易的购买方，可于任意时刻在任何主机上进入市场，以特定的条件购买特定的商品。Manager负责调节双方，协助交易的进行。要求： Buyer通过迁移进行比价，从报价最便宜的Seller处购买商品；
Buyer和Seller通过多次交互完成询价和交易； Manager可以帮助Buyer寻找Seller或帮助Seller寻找
Buyer，同时监管所有交易过程。51